BMC/Intel-BMC/linux.git/arch/x86/kernel/fpu/xstate.c, branch dev

x86/fpu: Fix double-increment in setup_xstate_features()

2015-06-12T08:48:12+00:00

I noticed that my MPX tracepoints were producing garbage for the lower and upper bounds: mpx_bounds_register_exception: address referenced: 0x00007fffffffccb7 bounds: lower: 0x0 ~upper: 0xffffffffffffffff mpx_bounds_register_exception: address referenced: 0x00007fffffffccbf bounds: lower: 0x0 ~upper: 0xffffffffffffffff This is, of course, bogus because 0x00007fffffffccbf is *within* the bounds. I assumed that my instruction decoder was bad and went looking at it. But I eventually realized that I was getting a '0' offset back from xstate_offsets[BNDREGS]. It was being skipped in the initialization, which is obviously bogus, so remove the extra leaf++. This also goes an initializes xstate_offsets/sizes[] to -1 so so that bugs like this will oops instead of silently failing in interesting ways. This was introduced by: 39f1acd ("x86/fpu/xstate: Don't assume the first zero xfeatures zero bit means the end") Signed-off-by: Dave Hansen Cc: Andrew Morton Cc: Andy Lutomirski Cc: Borislav Petkov Cc: Brian Gerst Cc: Denys Vlasenko Cc: H. Peter Anvin Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: dave@sr71.net Link: http://lkml.kernel.org/r/20150611193400.2E0B00DB@viggo.jf.intel.com Signed-off-by: Ingo Molnar

x86/fpu/xstate: Wrap get_xsave_addr() to make it safer

2015-06-09T10:24:29+00:00

The MPX code appears is calling a low-level FPU function (copy_fpregs_to_fpstate()). This function is not able to be called in all contexts, although it is safe to call directly in some cases. Although probably correct, the current code is ugly and potentially error-prone. So, add a wrapper that calls the (slightly) higher-level fpu__save() (which is preempt- safe) and also ensures that we even *have* an FPU context (in the case that this was called when in lazy FPU mode). Ingo had this to say about the details about when we need preemption disabled: > it's indeed generally unsafe to access/copy FPU registers with preemption enabled, > for two reasons: > > - on older systems that use FSAVE the instruction destroys FPU register > contents, which has to be handled carefully > > - even on newer systems if we copy to FPU registers (which this code doesn't) > then we don't want a context switch to occur in the middle of it, because a > context switch will write to the fpstate, potentially overwriting our new data > with old FPU state. > > But it's safe to access FPU registers with preemption enabled in a couple of > special cases: > > - potentially destructively saving FPU registers: the signal handling code does > this in copy_fpstate_to_sigframe(), because it can rely on the signal restore > side to restore the original FPU state. > > - reading FPU registers on modern systems: we don't do this anywhere at the > moment, mostly to keep symmetry with older systems where FSAVE is > destructive. > > - initializing FPU registers on modern systems: fpu__clear() does this. Here > it's safe because we don't copy from the fpstate. > > - directly writing FPU registers from user-space memory (!). We do this in > fpu__restore_sig(), and it's safe because neither context switches nor > irq-handler FPU use can corrupt the source context of the copy (which is > user-space memory). > > Note that the MPX code's current use of copy_fpregs_to_fpstate() was safe I think, > because: > > - MPX is predicated on eagerfpu, so the destructive F[N]SAVE instruction won't be > used. > > - the code was only reading FPU registers, and was doing it only in places that > guaranteed that an FPU state was already active (i.e. didn't do it in > kthreads) Signed-off-by: Dave Hansen Reviewed-by: Thomas Gleixner Cc: Andrew Morton Cc: Andy Lutomirski Cc: Dave Hansen Cc: Fenghua Yu Cc: H. Peter Anvin Cc: Linus Torvalds Cc: Oleg Nesterov Cc: Peter Zijlstra Cc: Rik van Riel Cc: Suresh Siddha Cc: bp@alien8.de Link: http://lkml.kernel.org/r/20150607183700.AA881696@viggo.jf.intel.com Signed-off-by: Ingo Molnar

x86/fpu/xstate: Fix up bad get_xsave_addr() assumptions

2015-06-09T10:24:29+00:00

get_xsave_addr() assumes that if an xsave bit is present in the hardware (pcntxt_mask) that it is present in a given xsave buffer. Due to an bug in the xsave code on all of the systems that have MPX (and thus all the users of this code), that has been a true assumption. But, the bug is getting fixed, so our assumption is not going to hold any more. It's quite possible (and normal) for an enabled state to be present on 'pcntxt_mask', but *not* in 'xstate_bv'. We need to consult 'xstate_bv'. Signed-off-by: Dave Hansen Reviewed-by: Thomas Gleixner Cc: Andrew Morton Cc: Dave Hansen Cc: H. Peter Anvin Cc: Linus Torvalds Cc: Peter Zijlstra Link: http://lkml.kernel.org/r/20150607183700.1E739B34@viggo.jf.intel.com Signed-off-by: Ingo Molnar

x86/fpu: Simplify copy_kernel_to_xregs_booting()

2015-05-27T12:11:33+00:00

copy_kernel_to_xregs_booting() has a second parameter that is the mask of xfeatures that should be copied - but this parameter is always -1. Simplify the call site of this function, this also makes it more similar to the function call signature of other copy_kernel_to*regs() functions. Cc: Andy Lutomirski Cc: Bobby Powers Cc: Borislav Petkov Cc: Dave Hansen Cc: Fenghua Yu Cc: H. Peter Anvin Cc: Linus Torvalds Cc: Oleg Nesterov Cc: Thomas Gleixner Signed-off-by: Ingo Molnar

x86/fpu: Fix fpu__init_system_xstate() comments

2015-05-25T10:49:34+00:00

Remove obsolete comment about __init limitations: in the new code there aren't any. Also standardize the comment style in the function while at it. Cc: Andy Lutomirski Cc: Borislav Petkov Cc: Dave Hansen Cc: Fenghua Yu Cc: H. Peter Anvin Cc: Linus Torvalds Cc: Oleg Nesterov Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: linux-kernel@vger.kernel.org Signed-off-by: Ingo Molnar

x86/fpu: Add CONFIG_X86_DEBUG_FPU=y FPU debugging code

2015-05-19T13:48:12+00:00

There are various internal FPU state debugging checks that never trigger in practice, but which are useful for FPU code development. Separate these out into CONFIG_X86_DEBUG_FPU=y, and also add a couple of new ones. The size difference is about 0.5K of code on defconfig: text data bss filename 15028906 2578816 1638400 vmlinux 15029430 2578816 1638400 vmlinux ( Keep this enabled by default until the new FPU code is debugged. ) Cc: Andy Lutomirski Cc: Borislav Petkov Cc: Dave Hansen Cc: Fenghua Yu Cc: H. Peter Anvin Cc: Linus Torvalds Cc: Oleg Nesterov Cc: Peter Zijlstra Cc: Thomas Gleixner Signed-off-by: Ingo Molnar

x86/fpu/init: Propagate __init annotations

2015-05-19T13:48:11+00:00

Now that all the FPU init function call dependencies are cleaned up we can propagate __init annotations deeper. This shrinks the runtime size of the kernel a bit, and also addresses a few section warnings. Cc: Andy Lutomirski Cc: Borislav Petkov Cc: Dave Hansen Cc: Fenghua Yu Cc: H. Peter Anvin Cc: Linus Torvalds Cc: Oleg Nesterov Cc: Peter Zijlstra Cc: Thomas Gleixner Signed-off-by: Ingo Molnar

x86/fpu/xstate: Clean up setup_xstate_comp() call

2015-05-19T13:48:11+00:00

So call setup_xstate_comp() from the xstate init code, not from the generic fpu__init_system() code. This allows us to remove the protytype from xstate.h as well. Cc: Andy Lutomirski Cc: Borislav Petkov Cc: Dave Hansen Cc: Fenghua Yu Cc: H. Peter Anvin Cc: Linus Torvalds Cc: Oleg Nesterov Cc: Peter Zijlstra Cc: Thomas Gleixner Signed-off-by: Ingo Molnar

x86/fpu/xstate: Don't assume the first zero xfeatures zero bit means the end

2015-05-19T13:48:10+00:00

The current xstate code in setup_xstate_features() assumes that the first zero bit means the end of xfeatures - but that is not so, the SDM clearly states that an arbitrary set of xfeatures might be enabled - and it is also clear from the description of the compaction feature that holes are possible: "13-6 Vol. 1MANAGING STATE USING THE XSAVE FEATURE SET [...] Compacted format. Each state component i (i ≥ 2) is located at a byte offset from the base address of the XSAVE area based on the XCOMP_BV field in the XSAVE header: — If XCOMP_BV[i] = 0, state component i is not in the XSAVE area. — If XCOMP_BV[i] = 1, the following items apply: • If XCOMP_BV[j] = 0 for every j, 2 ≤ j < i, state component i is located at a byte offset 576 from the base address of the XSAVE area. (This item applies if i is the first bit set in bits 62:2 of the XCOMP_BV; it implies that state component i is located at the beginning of the extended region.) • Otherwise, let j, 2 ≤ j < i, be the greatest value such that XCOMP_BV[j] = 1. Then state component i is located at a byte offset X from the location of state component j, where X is the number of bytes required for state component j as enumerated in CPUID.(EAX=0DH,ECX=j):EAX. (This item implies that state component i immediately follows the preceding state component whose bit is set in XCOMP_BV.)" So don't assume that the first zero xfeatures bit means the end of all xfeatures - iterate through all of them. I'm not aware of hardware that triggers this currently. Cc: Andy Lutomirski Cc: Borislav Petkov Cc: Dave Hansen Cc: Fenghua Yu Cc: H. Peter Anvin Cc: Linus Torvalds Cc: Oleg Nesterov Cc: Peter Zijlstra Cc: Thomas Gleixner Signed-off-by: Ingo Molnar

x86/fpu: Change fpu->fpregs_active from 'int' to 'char', add lazy switching comments

2015-05-19T13:48:09+00:00

Improve the memory layout of 'struct fpu': - change ->fpregs_active from 'int' to 'char' - it's just a single flag and modern x86 CPUs can do efficient byte accesses. - pack related fields closer to each other: often 'fpu->state' will not be touched, while the other fields will - so pack them into a group. Also add comments to each field, describing their purpose, and add some background information about lazy restores. Also fix an obsolete, lazy switching related comment in fpu_copy()'s description. Cc: Andy Lutomirski Cc: Borislav Petkov Cc: Dave Hansen Cc: Fenghua Yu Cc: H. Peter Anvin Cc: Linus Torvalds Cc: Oleg Nesterov Cc: Peter Zijlstra Cc: Thomas Gleixner Signed-off-by: Ingo Molnar