diff options
Diffstat (limited to 'drivers/lguest/core.c')
| -rw-r--r-- | drivers/lguest/core.c | 357 |
1 files changed, 333 insertions, 24 deletions
diff --git a/drivers/lguest/core.c b/drivers/lguest/core.c index ce909ec57499..0a46e8837d9a 100644 --- a/drivers/lguest/core.c +++ b/drivers/lguest/core.c @@ -1,5 +1,8 @@ -/* World's simplest hypervisor, to test paravirt_ops and show - * unbelievers that virtualization is the future. Plus, it's fun! */ +/*P:400 This contains run_guest() which actually calls into the Host<->Guest + * Switcher and analyzes the return, such as determining if the Guest wants the + * Host to do something. This file also contains useful helper routines, and a + * couple of non-obvious setup and teardown pieces which were implemented after + * days of debugging pain. :*/ #include <linux/module.h> #include <linux/stringify.h> #include <linux/stddef.h> @@ -61,11 +64,33 @@ static struct lguest_pages *lguest_pages(unsigned int cpu) (SWITCHER_ADDR + SHARED_SWITCHER_PAGES*PAGE_SIZE))[cpu]); } +/*H:010 We need to set up the Switcher at a high virtual address. Remember the + * Switcher is a few hundred bytes of assembler code which actually changes the + * CPU to run the Guest, and then changes back to the Host when a trap or + * interrupt happens. + * + * The Switcher code must be at the same virtual address in the Guest as the + * Host since it will be running as the switchover occurs. + * + * Trying to map memory at a particular address is an unusual thing to do, so + * it's not a simple one-liner. We also set up the per-cpu parts of the + * Switcher here. + */ static __init int map_switcher(void) { int i, err; struct page **pagep; + /* + * Map the Switcher in to high memory. + * + * It turns out that if we choose the address 0xFFC00000 (4MB under the + * top virtual address), it makes setting up the page tables really + * easy. + */ + + /* We allocate an array of "struct page"s. map_vm_area() wants the + * pages in this form, rather than just an array of pointers. */ switcher_page = kmalloc(sizeof(switcher_page[0])*TOTAL_SWITCHER_PAGES, GFP_KERNEL); if (!switcher_page) { @@ -73,6 +98,8 @@ static __init int map_switcher(void) goto out; } + /* Now we actually allocate the pages. The Guest will see these pages, + * so we make sure they're zeroed. */ for (i = 0; i < TOTAL_SWITCHER_PAGES; i++) { unsigned long addr = get_zeroed_page(GFP_KERNEL); if (!addr) { @@ -82,6 +109,9 @@ static __init int map_switcher(void) switcher_page[i] = virt_to_page(addr); } + /* Now we reserve the "virtual memory area" we want: 0xFFC00000 + * (SWITCHER_ADDR). We might not get it in theory, but in practice + * it's worked so far. */ switcher_vma = __get_vm_area(TOTAL_SWITCHER_PAGES * PAGE_SIZE, VM_ALLOC, SWITCHER_ADDR, VMALLOC_END); if (!switcher_vma) { @@ -90,49 +120,105 @@ static __init int map_switcher(void) goto free_pages; } + /* This code actually sets up the pages we've allocated to appear at + * SWITCHER_ADDR. map_vm_area() takes the vma we allocated above, the + * kind of pages we're mapping (kernel pages), and a pointer to our + * array of struct pages. It increments that pointer, but we don't + * care. */ pagep = switcher_page; err = map_vm_area(switcher_vma, PAGE_KERNEL, &pagep); if (err) { printk("lguest: map_vm_area failed: %i\n", err); goto free_vma; } + + /* Now the switcher is mapped at the right address, we can't fail! + * Copy in the compiled-in Switcher code (from switcher.S). */ memcpy(switcher_vma->addr, start_switcher_text, end_switcher_text - start_switcher_text); - /* Fix up IDT entries to point into copied text. */ + /* Most of the switcher.S doesn't care that it's been moved; on Intel, + * jumps are relative, and it doesn't access any references to external + * code or data. + * + * The only exception is the interrupt handlers in switcher.S: their + * addresses are placed in a table (default_idt_entries), so we need to + * update the table with the new addresses. switcher_offset() is a + * convenience function which returns the distance between the builtin + * switcher code and the high-mapped copy we just made. */ for (i = 0; i < IDT_ENTRIES; i++) default_idt_entries[i] += switcher_offset(); + /* + * Set up the Switcher's per-cpu areas. + * + * Each CPU gets two pages of its own within the high-mapped region + * (aka. "struct lguest_pages"). Much of this can be initialized now, + * but some depends on what Guest we are running (which is set up in + * copy_in_guest_info()). + */ for_each_possible_cpu(i) { + /* lguest_pages() returns this CPU's two pages. */ struct lguest_pages *pages = lguest_pages(i); + /* This is a convenience pointer to make the code fit one + * statement to a line. */ struct lguest_ro_state *state = &pages->state; - /* These fields are static: rest done in copy_in_guest_info */ + /* The Global Descriptor Table: the Host has a different one + * for each CPU. We keep a descriptor for the GDT which says + * where it is and how big it is (the size is actually the last + * byte, not the size, hence the "-1"). */ state->host_gdt_desc.size = GDT_SIZE-1; state->host_gdt_desc.address = (long)get_cpu_gdt_table(i); + + /* All CPUs on the Host use the same Interrupt Descriptor + * Table, so we just use store_idt(), which gets this CPU's IDT + * descriptor. */ store_idt(&state->host_idt_desc); + + /* The descriptors for the Guest's GDT and IDT can be filled + * out now, too. We copy the GDT & IDT into ->guest_gdt and + * ->guest_idt before actually running the Guest. */ state->guest_idt_desc.size = sizeof(state->guest_idt)-1; state->guest_idt_desc.address = (long)&state->guest_idt; state->guest_gdt_desc.size = sizeof(state->guest_gdt)-1; state->guest_gdt_desc.address = (long)&state->guest_gdt; + + /* We know where we want the stack to be when the Guest enters + * the switcher: in pages->regs. The stack grows upwards, so + * we start it at the end of that structure. */ state->guest_tss.esp0 = (long)(&pages->regs + 1); + /* And this is the GDT entry to use for the stack: we keep a + * couple of special LGUEST entries. */ state->guest_tss.ss0 = LGUEST_DS; - /* No I/O for you! */ + + /* x86 can have a finegrained bitmap which indicates what I/O + * ports the process can use. We set it to the end of our + * structure, meaning "none". */ state->guest_tss.io_bitmap_base = sizeof(state->guest_tss); + + /* Some GDT entries are the same across all Guests, so we can + * set them up now. */ setup_default_gdt_entries(state); + /* Most IDT entries are the same for all Guests, too.*/ setup_default_idt_entries(state, default_idt_entries); - /* Setup LGUEST segments on all cpus */ + /* The Host needs to be able to use the LGUEST segments on this + * CPU, too, so put them in the Host GDT. */ get_cpu_gdt_table(i)[GDT_ENTRY_LGUEST_CS] = FULL_EXEC_SEGMENT; get_cpu_gdt_table(i)[GDT_ENTRY_LGUEST_DS] = FULL_SEGMENT; } - /* Initialize entry point into switcher. */ + /* In the Switcher, we want the %cs segment register to use the + * LGUEST_CS GDT entry: we've put that in the Host and Guest GDTs, so + * it will be undisturbed when we switch. To change %cs and jump we + * need this structure to feed to Intel's "lcall" instruction. */ lguest_entry.offset = (long)switch_to_guest + switcher_offset(); lguest_entry.segment = LGUEST_CS; printk(KERN_INFO "lguest: mapped switcher at %p\n", switcher_vma->addr); + /* And we succeeded... */ return 0; free_vma: @@ -146,35 +232,58 @@ free_some_pages: out: return err; } +/*:*/ +/* Cleaning up the mapping when the module is unloaded is almost... + * too easy. */ static void unmap_switcher(void) { unsigned int i; + /* vunmap() undoes *both* map_vm_area() and __get_vm_area(). */ vunmap(switcher_vma->addr); + /* Now we just need to free the pages we copied the switcher into */ for (i = 0; i < TOTAL_SWITCHER_PAGES; i++) __free_pages(switcher_page[i], 0); } -/* IN/OUT insns: enough to get us past boot-time probing. */ +/*H:130 Our Guest is usually so well behaved; it never tries to do things it + * isn't allowed to. Unfortunately, "struct paravirt_ops" isn't quite + * complete, because it doesn't contain replacements for the Intel I/O + * instructions. As a result, the Guest sometimes fumbles across one during + * the boot process as it probes for various things which are usually attached + * to a PC. + * + * When the Guest uses one of these instructions, we get trap #13 (General + * Protection Fault) and come here. We see if it's one of those troublesome + * instructions and skip over it. We return true if we did. */ static int emulate_insn(struct lguest *lg) { u8 insn; unsigned int insnlen = 0, in = 0, shift = 0; + /* The eip contains the *virtual* address of the Guest's instruction: + * guest_pa just subtracts the Guest's page_offset. */ unsigned long physaddr = guest_pa(lg, lg->regs->eip); - /* This only works for addresses in linear mapping... */ + /* The guest_pa() function only works for Guest kernel addresses, but + * that's all we're trying to do anyway. */ if (lg->regs->eip < lg->page_offset) return 0; + + /* Decoding x86 instructions is icky. */ lgread(lg, &insn, physaddr, 1); - /* Operand size prefix means it's actually for ax. */ + /* 0x66 is an "operand prefix". It means it's using the upper 16 bits + of the eax register. */ if (insn == 0x66) { shift = 16; + /* The instruction is 1 byte so far, read the next byte. */ insnlen = 1; lgread(lg, &insn, physaddr + insnlen, 1); } + /* We can ignore the lower bit for the moment and decode the 4 opcodes + * we need to emulate. */ switch (insn & 0xFE) { case 0xE4: /* in <next byte>,%al */ insnlen += 2; @@ -191,9 +300,13 @@ static int emulate_insn(struct lguest *lg) insnlen += 1; break; default: + /* OK, we don't know what this is, can't emulate. */ return 0; } + /* If it was an "IN" instruction, they expect the result to be read + * into %eax, so we change %eax. We always return all-ones, which + * traditionally means "there's nothing there". */ if (in) { /* Lower bit tells is whether it's a 16 or 32 bit access */ if (insn & 0x1) @@ -201,28 +314,46 @@ static int emulate_insn(struct lguest *lg) else lg->regs->eax |= (0xFFFF << shift); } + /* Finally, we've "done" the instruction, so move past it. */ lg->regs->eip += insnlen; + /* Success! */ return 1; } - +/*:*/ + +/*L:305 + * Dealing With Guest Memory. + * + * When the Guest gives us (what it thinks is) a physical address, we can use + * the normal copy_from_user() & copy_to_user() on that address: remember, + * Guest physical == Launcher virtual. + * + * But we can't trust the Guest: it might be trying to access the Launcher + * code. We have to check that the range is below the pfn_limit the Launcher + * gave us. We have to make sure that addr + len doesn't give us a false + * positive by overflowing, too. */ int lguest_address_ok(const struct lguest *lg, unsigned long addr, unsigned long len) { return (addr+len) / PAGE_SIZE < lg->pfn_limit && (addr+len >= addr); } -/* Just like get_user, but don't let guest access lguest binary. */ +/* This is a convenient routine to get a 32-bit value from the Guest (a very + * common operation). Here we can see how useful the kill_lguest() routine we + * met in the Launcher can be: we return a random value (0) instead of needing + * to return an error. */ u32 lgread_u32(struct lguest *lg, unsigned long addr) { u32 val = 0; - /* Don't let them access lguest binary */ + /* Don't let them access lguest binary. */ if (!lguest_address_ok(lg, addr, sizeof(val)) || get_user(val, (u32 __user *)addr) != 0) kill_guest(lg, "bad read address %#lx", addr); return val; } +/* Same thing for writing a value. */ void lgwrite_u32(struct lguest *lg, unsigned long addr, u32 val) { if (!lguest_address_ok(lg, addr, sizeof(val)) @@ -230,6 +361,9 @@ void lgwrite_u32(struct lguest *lg, unsigned long addr, u32 val) kill_guest(lg, "bad write address %#lx", addr); } +/* This routine is more generic, and copies a range of Guest bytes into a + * buffer. If the copy_from_user() fails, we fill the buffer with zeroes, so + * the caller doesn't end up using uninitialized kernel memory. */ void lgread(struct lguest *lg, void *b, unsigned long addr, unsigned bytes) { if (!lguest_address_ok(lg, addr, bytes) @@ -240,6 +374,7 @@ void lgread(struct lguest *lg, void *b, unsigned long addr, unsigned bytes) } } +/* Similarly, our generic routine to copy into a range of Guest bytes. */ void lgwrite(struct lguest *lg, unsigned long addr, const void *b, unsigned bytes) { @@ -247,6 +382,7 @@ void lgwrite(struct lguest *lg, unsigned long addr, const void *b, || copy_to_user((void __user *)addr, b, bytes) != 0) kill_guest(lg, "bad write address %#lx len %u", addr, bytes); } +/* (end of memory access helper routines) :*/ static void set_ts(void) { @@ -257,54 +393,108 @@ static void set_ts(void) write_cr0(cr0|8); } +/*S:010 + * We are getting close to the Switcher. + * + * Remember that each CPU has two pages which are visible to the Guest when it + * runs on that CPU. This has to contain the state for that Guest: we copy the + * state in just before we run the Guest. + * + * Each Guest has "changed" flags which indicate what has changed in the Guest + * since it last ran. We saw this set in interrupts_and_traps.c and + * segments.c. + */ static void copy_in_guest_info(struct lguest *lg, struct lguest_pages *pages) { + /* Copying all this data can be quite expensive. We usually run the + * same Guest we ran last time (and that Guest hasn't run anywhere else + * meanwhile). If that's not the case, we pretend everything in the + * Guest has changed. */ if (__get_cpu_var(last_guest) != lg || lg->last_pages != pages) { __get_cpu_var(last_guest) = lg; lg->last_pages = pages; lg->changed = CHANGED_ALL; } - /* These are pretty cheap, so we do them unconditionally. */ + /* These copies are pretty cheap, so we do them unconditionally: */ + /* Save the current Host top-level page directory. */ pages->state.host_cr3 = __pa(current->mm->pgd); + /* Set up the Guest's page tables to see this CPU's pages (and no + * other CPU's pages). */ map_switcher_in_guest(lg, pages); + /* Set up the two "TSS" members which tell the CPU what stack to use + * for traps which do directly into the Guest (ie. traps at privilege + * level 1). */ pages->state.guest_tss.esp1 = lg->esp1; pages->state.guest_tss.ss1 = lg->ss1; - /* Copy direct trap entries. */ + /* Copy direct-to-Guest trap entries. */ if (lg->changed & CHANGED_IDT) copy_traps(lg, pages->state.guest_idt, default_idt_entries); - /* Copy all GDT entries but the TSS. */ + /* Copy all GDT entries which the Guest can change. */ if (lg->changed & CHANGED_GDT) copy_gdt(lg, pages->state.guest_gdt); /* If only the TLS entries have changed, copy them. */ else if (lg->changed & CHANGED_GDT_TLS) copy_gdt_tls(lg, pages->state.guest_gdt); + /* Mark the Guest as unchanged for next time. */ lg->changed = 0; } +/* Finally: the code to actually call into the Switcher to run the Guest. */ static void run_guest_once(struct lguest *lg, struct lguest_pages *pages) { + /* This is a dummy value we need for GCC's sake. */ unsigned int clobber; + /* Copy the guest-specific information into this CPU's "struct + * lguest_pages". */ copy_in_guest_info(lg, pages); - /* Put eflags on stack, lcall does rest: suitable for iret return. */ + /* Now: we push the "eflags" register on the stack, then do an "lcall". + * This is how we change from using the kernel code segment to using + * the dedicated lguest code segment, as well as jumping into the + * Switcher. + * + * The lcall also pushes the old code segment (KERNEL_CS) onto the + * stack, then the address of this call. This stack layout happens to + * exactly match the stack of an interrupt... */ asm volatile("pushf; lcall *lguest_entry" + /* This is how we tell GCC that %eax ("a") and %ebx ("b") + * are changed by this routine. The "=" means output. */ : "=a"(clobber), "=b"(clobber) + /* %eax contains the pages pointer. ("0" refers to the + * 0-th argument above, ie "a"). %ebx contains the + * physical address of the Guest's top-level page + * directory. */ : "0"(pages), "1"(__pa(lg->pgdirs[lg->pgdidx].pgdir)) + /* We tell gcc that all these registers could change, + * which means we don't have to save and restore them in + * the Switcher. */ : "memory", "%edx", "%ecx", "%edi", "%esi"); } +/*:*/ +/*H:030 Let's jump straight to the the main loop which runs the Guest. + * Remember, this is called by the Launcher reading /dev/lguest, and we keep + * going around and around until something interesting happens. */ int run_guest(struct lguest *lg, unsigned long __user *user) { + /* We stop running once the Guest is dead. */ while (!lg->dead) { + /* We need to initialize this, otherwise gcc complains. It's + * not (yet) clever enough to see that it's initialized when we + * need it. */ unsigned int cr2 = 0; /* Damn gcc */ - /* Hypercalls first: we might have been out to userspace */ + /* First we run any hypercalls the Guest wants done: either in + * the hypercall ring in "struct lguest_data", or directly by + * using int 31 (LGUEST_TRAP_ENTRY). */ do_hypercalls(lg); + /* It's possible the Guest did a SEND_DMA hypercall to the + * Launcher, in which case we return from the read() now. */ if (lg->dma_is_pending) { if (put_user(lg->pending_dma, user) || put_user(lg->pending_key, user+1)) @@ -312,6 +502,7 @@ int run_guest(struct lguest *lg, unsigned long __user *user) return sizeof(unsigned long)*2; } + /* Check for signals */ if (signal_pending(current)) return -ERESTARTSYS; @@ -319,77 +510,154 @@ int run_guest(struct lguest *lg, unsigned long __user *user) if (lg->break_out) return -EAGAIN; + /* Check if there are any interrupts which can be delivered + * now: if so, this sets up the hander to be executed when we + * next run the Guest. */ maybe_do_interrupt(lg); + /* All long-lived kernel loops need to check with this horrible + * thing called the freezer. If the Host is trying to suspend, + * it stops us. */ try_to_freeze(); + /* Just make absolutely sure the Guest is still alive. One of + * those hypercalls could have been fatal, for example. */ if (lg->dead) break; + /* If the Guest asked to be stopped, we sleep. The Guest's + * clock timer or LHCALL_BREAK from the Waker will wake us. */ if (lg->halted) { set_current_state(TASK_INTERRUPTIBLE); schedule(); continue; } + /* OK, now we're ready to jump into the Guest. First we put up + * the "Do Not Disturb" sign: */ local_irq_disable(); - /* Even if *we* don't want FPU trap, guest might... */ + /* Remember the awfully-named TS bit? If the Guest has asked + * to set it we set it now, so we can trap and pass that trap + * to the Guest if it uses the FPU. */ if (lg->ts) set_ts(); - /* Don't let Guest do SYSENTER: we can't handle it. */ + /* SYSENTER is an optimized way of doing system calls. We + * can't allow it because it always jumps to privilege level 0. + * A normal Guest won't try it because we don't advertise it in + * CPUID, but a malicious Guest (or malicious Guest userspace + * program) could, so we tell the CPU to disable it before + * running the Guest. */ if (boot_cpu_has(X86_FEATURE_SEP)) wrmsr(MSR_IA32_SYSENTER_CS, 0, 0); + /* Now we actually run the Guest. It will pop back out when + * something interesting happens, and we can examine its + * registers to see what it was doing. */ run_guest_once(lg, lguest_pages(raw_smp_processor_id())); - /* Save cr2 now if we page-faulted. */ + /* The "regs" pointer contains two extra entries which are not + * really registers: a trap number which says what interrupt or + * trap made the switcher code come back, and an error code + * which some traps set. */ + + /* If the Guest page faulted, then the cr2 register will tell + * us the bad virtual address. We have to grab this now, + * because once we re-enable interrupts an interrupt could + * fault and thus overwrite cr2, or we could even move off to a + * different CPU. */ if (lg->regs->trapnum == 14) cr2 = read_cr2(); + /* Similarly, if we took a trap because the Guest used the FPU, + * we have to restore the FPU it expects to see. */ else if (lg->regs->trapnum == 7) math_state_restore(); + /* Restore SYSENTER if it's supposed to be on. */ if (boot_cpu_has(X86_FEATURE_SEP)) wrmsr(MSR_IA32_SYSENTER_CS, __KERNEL_CS, 0); + + /* Now we're ready to be interrupted or moved to other CPUs */ local_irq_enable(); + /* OK, so what happened? */ switch (lg->regs->trapnum) { case 13: /* We've intercepted a GPF. */ + /* Check if this was one of those annoying IN or OUT + * instructions which we need to emulate. If so, we + * just go back into the Guest after we've done it. */ if (lg->regs->errcode == 0) { if (emulate_insn(lg)) continue; } break; case 14: /* We've intercepted a page fault. */ + /* The Guest accessed a virtual address that wasn't + * mapped. This happens a lot: we don't actually set + * up most of the page tables for the Guest at all when + * we start: as it runs it asks for more and more, and + * we set them up as required. In this case, we don't + * even tell the Guest that the fault happened. + * + * The errcode tells whether this was a read or a + * write, and whether kernel or userspace code. */ if (demand_page(lg, cr2, lg->regs->errcode)) continue; - /* If lguest_data is NULL, this won't hurt. */ + /* OK, it's really not there (or not OK): the Guest + * needs to know. We write out the cr2 value so it + * knows where the fault occurred. + * + * Note that if the Guest were really messed up, this + * could happen before it's done the INITIALIZE + * hypercall, so lg->lguest_data will be NULL, so + * &lg->lguest_data->cr2 will be address 8. Writing + * into that address won't hurt the Host at all, + * though. */ if (put_user(cr2, &lg->lguest_data->cr2)) kill_guest(lg, "Writing cr2"); break; case 7: /* We've intercepted a Device Not Available fault. */ - /* If they don't want to know, just absorb it. */ + /* If the Guest doesn't want to know, we already + * restored the Floating Point Unit, so we just + * continue without telling it. */ if (!lg->ts) continue; break; - case 32 ... 255: /* Real interrupt, fall thru */ + case 32 ... 255: + /* These values mean a real interrupt occurred, in + * which case the Host handler has already been run. + * We just do a friendly check if another process + * should now be run, then fall through to loop + * around: */ cond_resched(); case LGUEST_TRAP_ENTRY: /* Handled at top of loop */ continue; } + /* If we get here, it's a trap the Guest wants to know + * about. */ if (deliver_trap(lg, lg->regs->trapnum)) continue; + /* If the Guest doesn't have a handler (either it hasn't + * registered any yet, or it's one of the faults we don't let + * it handle), it dies with a cryptic error message. */ kill_guest(lg, "unhandled trap %li at %#lx (%#lx)", lg->regs->trapnum, lg->regs->eip, lg->regs->trapnum == 14 ? cr2 : lg->regs->errcode); } + /* The Guest is dead => "No such file or directory" */ return -ENOENT; } +/* Now we can look at each of the routines this calls, in increasing order of + * complexity: do_hypercalls(), emulate_insn(), maybe_do_interrupt(), + * deliver_trap() and demand_page(). After all those, we'll be ready to + * examine the Switcher, and our philosophical understanding of the Host/Guest + * duality will be complete. :*/ + int find_free_guest(void) { unsigned int i; @@ -407,55 +675,96 @@ static void adjust_pge(void *on) write_cr4(read_cr4() & ~X86_CR4_PGE); } +/*H:000 + * Welcome to the Host! + * + * By this point your brain has been tickled by the Guest code and numbed by + * the Launcher code; prepare for it to be stretched by the Host code. This is + * the heart. Let's begin at the initialization routine for the Host's lg + * module. + */ static int __init init(void) { int err; + /* Lguest can't run under Xen, VMI or itself. It does Tricky Stuff. */ if (paravirt_enabled()) { printk("lguest is afraid of %s\n", paravirt_ops.name); return -EPERM; } + /* First we put the Switcher up in very high virtual memory. */ err = map_switcher(); if (err) return err; + /* Now we set up the pagetable implementation for the Guests. */ err = init_pagetables(switcher_page, SHARED_SWITCHER_PAGES); if (err) { unmap_switcher(); return err; } + + /* The I/O subsystem needs some things initialized. */ lguest_io_init(); + /* /dev/lguest needs to be registered. */ err = lguest_device_init(); if (err) { free_pagetables(); unmap_switcher(); return err; } + + /* Finally, we need to turn off "Page Global Enable". PGE is an + * optimization where page table entries are specially marked to show + * they never change. The Host kernel marks all the kernel pages this + * way because it's always present, even when userspace is running. + * + * Lguest breaks this: unbeknownst to the rest of the Host kernel, we + * switch to the Guest kernel. If you don't disable this on all CPUs, + * you'll get really weird bugs that you'll chase for two days. + * + * I used to turn PGE off every time we switched to the Guest and back + * on when we return, but that slowed the Switcher down noticibly. */ + + /* We don't need the complexity of CPUs coming and going while we're + * doing this. */ lock_cpu_hotplug(); if (cpu_has_pge) { /* We have a broader idea of "global". */ + /* Remember that this was originally set (for cleanup). */ cpu_had_pge = 1; + /* adjust_pge is a helper function which sets or unsets the PGE + * bit on its CPU, depending on the argument (0 == unset). */ on_each_cpu(adjust_pge, (void *)0, 0, 1); + /* Turn off the feature in the global feature set. */ clear_bit(X86_FEATURE_PGE, boot_cpu_data.x86_capability); } unlock_cpu_hotplug(); + + /* All good! */ return 0; } +/* Cleaning up is just the same code, backwards. With a little French. */ static void __exit fini(void) { lguest_device_remove(); free_pagetables(); unmap_switcher(); + + /* If we had PGE before we started, turn it back on now. */ lock_cpu_hotplug(); if (cpu_had_pge) { set_bit(X86_FEATURE_PGE, boot_cpu_data.x86_capability); + /* adjust_pge's argument "1" means set PGE. */ on_each_cpu(adjust_pge, (void *)1, 0, 1); } unlock_cpu_hotplug(); } +/* The Host side of lguest can be a module. This is a nice way for people to + * play with it. */ module_init(init); module_exit(fini); MODULE_LICENSE("GPL"); |