Commit-ID: 39f1acd243725b4b20caa37a81b6c8f641b505b8
Gitweb: http://git.kernel.org/tip/39f1acd243725b4b20caa37a81b6c8f641b505b8
Author: Ingo Molnar <mingo@xxxxxxxxxx>
AuthorDate: Mon, 4 May 2015 07:37:47 +0200
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Tue, 19 May 2015 15:48:10 +0200
x86/fpu/xstate: Don't assume the first zero xfeatures zero bit means the end
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 <luto@xxxxxxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Cc: Fenghua Yu <fenghua.yu@xxxxxxxxx>
Cc: H. Peter Anvin <hpa@xxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Oleg Nesterov <oleg@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
arch/x86/kernel/fpu/xstate.c | 17 +++++++++--------
1 file changed, 9 insertions(+), 8 deletions(-)
diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
index cd7f1a6..a024fa5 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)
--
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