From 39f1acd243725b4b20caa37a81b6c8f641b505b8 Mon Sep 17 00:00:00 2001 From: Ingo Molnar Date: Mon, 4 May 2015 07:37:47 +0200 Subject: x86/fpu/xstate: Don't assume the first zero xfeatures zero bit means the end MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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 --- arch/x86/kernel/fpu/xstate.c | 17 +++++++++-------- 1 file changed, 9 insertions(+), 8 deletions(-) (limited to 'arch/x86/kernel/fpu/xstate.c') diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c index cd7f1a6bd933..a024fa591a93 100644 --- a/arch/x86/kernel/fpu/xstate.c +++ b/arch/x86/kernel/fpu/xstate.c @@ -168,26 +168,27 @@ void fpu__init_cpu_xstate(void) } /* - * Record the offsets and sizes of different state managed by the xsave - * memory layout. + * Record the offsets and sizes of various xstates contained + * in the XSAVE state memory layout. + * + * ( Note that certain features might be non-present, for them + * we'll have 0 offset and 0 size. ) */ static void __init setup_xstate_features(void) { - int eax, ebx, ecx, edx, leaf = 0x2; + u32 eax, ebx, ecx, edx, leaf; xfeatures_nr = fls64(xfeatures_mask); - do { + for (leaf = 2; leaf < xfeatures_nr; leaf++) { cpuid_count(XSTATE_CPUID, leaf, &eax, &ebx, &ecx, &edx); - if (eax == 0) - break; - xstate_offsets[leaf] = ebx; xstate_sizes[leaf] = eax; + printk(KERN_INFO "x86/fpu: xstate_offset[%d]: %04x, xstate_sizes[%d]: %04x\n", leaf, ebx, leaf, eax); leaf++; - } while (1); + } } static void print_xstate_feature(u64 xstate_mask) -- cgit v1.2.3