From 0c4109bec0a6cde471bef3a21cd6f8384a614469 Mon Sep 17 00:00:00 2001 From: Dave Hansen Date: Sun, 7 Jun 2015 11:37:00 -0700 Subject: [PATCH] x86/fpu/xstate: Fix up bad get_xsave_addr() assumptions 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 --- arch/x86/kernel/fpu/xstate.c | 45 +++++++++++++++++++++++++++++------- 1 file changed, 37 insertions(+), 8 deletions(-) diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c index a580eb5c7e52..af3700e0dbd2 100644 --- a/arch/x86/kernel/fpu/xstate.c +++ b/arch/x86/kernel/fpu/xstate.c @@ -382,19 +382,48 @@ void fpu__resume_cpu(void) * This is the API that is called to get xstate address in either * standard format or compacted format of xsave area. * + * Note that if there is no data for the field in the xsave buffer + * this will return NULL. + * * Inputs: - * xsave: base address of the xsave area; - * xstate: state which is defined in xsave.h (e.g. XSTATE_FP, XSTATE_SSE, - * etc.) + * xstate: the thread's storage area for all FPU data + * xstate_feature: state which is defined in xsave.h (e.g. + * XSTATE_FP, XSTATE_SSE, etc...) * Output: - * address of the state in the xsave area. + * address of the state in the xsave area, or NULL if the + * field is not present in the xsave buffer. */ -void *get_xsave_addr(struct xregs_state *xsave, int xstate) +void *get_xsave_addr(struct xregs_state *xsave, int xstate_feature) { - int feature = fls64(xstate) - 1; - if (!test_bit(feature, (unsigned long *)&xfeatures_mask)) + int feature_nr = fls64(xstate_feature) - 1; + /* + * Do we even *have* xsave state? + */ + if (!boot_cpu_has(X86_FEATURE_XSAVE)) return NULL; - return (void *)xsave + xstate_comp_offsets[feature]; + xsave = ¤t->thread.fpu.state.xsave; + /* + * We should not ever be requesting features that we + * have not enabled. Remember that pcntxt_mask is + * what we write to the XCR0 register. + */ + WARN_ONCE(!(xfeatures_mask & xstate_feature), + "get of unsupported state"); + /* + * This assumes the last 'xsave*' instruction to + * have requested that 'xstate_feature' be saved. + * If it did not, we might be seeing and old value + * of the field in the buffer. + * + * This can happen because the last 'xsave' did not + * request that this feature be saved (unlikely) + * or because the "init optimization" caused it + * to not be saved. + */ + if (!(xsave->header.xfeatures & xstate_feature)) + return NULL; + + return (void *)xsave + xstate_comp_offsets[feature_nr]; } EXPORT_SYMBOL_GPL(get_xsave_addr);