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authorIngo Molnar <mingo@kernel.org>2019-11-29 10:17:25 +0300
committerIngo Molnar <mingo@kernel.org>2019-12-10 12:12:55 +0300
commit186525bd6b83efc592672e2d6185e4d7c810d2b4 (patch)
tree0fd5cb176e8e113a552730ea07dedbb8359e652b /arch/x86/kernel/ldt.c
parent1f059dfdf5d170dccbac92193be2fee3c1763384 (diff)
downloadlinux-186525bd6b83efc592672e2d6185e4d7c810d2b4.tar.xz
mm, x86/mm: Untangle address space layout definitions from basic pgtable type definitions
- Untangle the somewhat incestous way of how VMALLOC_START is used all across the kernel, but is, on x86, defined deep inside one of the lowest level page table headers. It doesn't help that vmalloc.h only includes a single asm header: #include <asm/page.h> /* pgprot_t */ So there was no existing cross-arch way to decouple address layout definitions from page.h details. I used this: #ifndef VMALLOC_START # include <asm/vmalloc.h> #endif This way every architecture that wants to simplify page.h can do so. - Also on x86 we had a couple of LDT related inline functions that used the late-stage address space layout positions - but these could be uninlined without real trouble - the end result is cleaner this way as well. Signed-off-by: Ingo Molnar <mingo@kernel.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Borislav Petkov <bp@alien8.de> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Rik van Riel <riel@redhat.com> Cc: linux-kernel@vger.kernel.org Cc: linux-mm@kvack.org Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'arch/x86/kernel/ldt.c')
-rw-r--r--arch/x86/kernel/ldt.c83
1 files changed, 83 insertions, 0 deletions
diff --git a/arch/x86/kernel/ldt.c b/arch/x86/kernel/ldt.c
index b2463fcb20a8..c57e1ca70fd1 100644
--- a/arch/x86/kernel/ldt.c
+++ b/arch/x86/kernel/ldt.c
@@ -28,6 +28,89 @@
#include <asm/desc.h>
#include <asm/mmu_context.h>
#include <asm/syscalls.h>
+#include <asm/pgtable_areas.h>
+
+/* This is a multiple of PAGE_SIZE. */
+#define LDT_SLOT_STRIDE (LDT_ENTRIES * LDT_ENTRY_SIZE)
+
+static inline void *ldt_slot_va(int slot)
+{
+ return (void *)(LDT_BASE_ADDR + LDT_SLOT_STRIDE * slot);
+}
+
+void load_mm_ldt(struct mm_struct *mm)
+{
+ struct ldt_struct *ldt;
+
+ /* READ_ONCE synchronizes with smp_store_release */
+ ldt = READ_ONCE(mm->context.ldt);
+
+ /*
+ * Any change to mm->context.ldt is followed by an IPI to all
+ * CPUs with the mm active. The LDT will not be freed until
+ * after the IPI is handled by all such CPUs. This means that,
+ * if the ldt_struct changes before we return, the values we see
+ * will be safe, and the new values will be loaded before we run
+ * any user code.
+ *
+ * NB: don't try to convert this to use RCU without extreme care.
+ * We would still need IRQs off, because we don't want to change
+ * the local LDT after an IPI loaded a newer value than the one
+ * that we can see.
+ */
+
+ if (unlikely(ldt)) {
+ if (static_cpu_has(X86_FEATURE_PTI)) {
+ if (WARN_ON_ONCE((unsigned long)ldt->slot > 1)) {
+ /*
+ * Whoops -- either the new LDT isn't mapped
+ * (if slot == -1) or is mapped into a bogus
+ * slot (if slot > 1).
+ */
+ clear_LDT();
+ return;
+ }
+
+ /*
+ * If page table isolation is enabled, ldt->entries
+ * will not be mapped in the userspace pagetables.
+ * Tell the CPU to access the LDT through the alias
+ * at ldt_slot_va(ldt->slot).
+ */
+ set_ldt(ldt_slot_va(ldt->slot), ldt->nr_entries);
+ } else {
+ set_ldt(ldt->entries, ldt->nr_entries);
+ }
+ } else {
+ clear_LDT();
+ }
+}
+
+void switch_ldt(struct mm_struct *prev, struct mm_struct *next)
+{
+ /*
+ * Load the LDT if either the old or new mm had an LDT.
+ *
+ * An mm will never go from having an LDT to not having an LDT. Two
+ * mms never share an LDT, so we don't gain anything by checking to
+ * see whether the LDT changed. There's also no guarantee that
+ * prev->context.ldt actually matches LDTR, but, if LDTR is non-NULL,
+ * then prev->context.ldt will also be non-NULL.
+ *
+ * If we really cared, we could optimize the case where prev == next
+ * and we're exiting lazy mode. Most of the time, if this happens,
+ * we don't actually need to reload LDTR, but modify_ldt() is mostly
+ * used by legacy code and emulators where we don't need this level of
+ * performance.
+ *
+ * This uses | instead of || because it generates better code.
+ */
+ if (unlikely((unsigned long)prev->context.ldt |
+ (unsigned long)next->context.ldt))
+ load_mm_ldt(next);
+
+ DEBUG_LOCKS_WARN_ON(preemptible());
+}
static void refresh_ldt_segments(void)
{