[PATCH v3 Bugfix 1/6] x86/xsave.c: Fix xstate offsets and sizes enumeration

[Fenghua Yu]

From: Fenghua Yu <fenghua.yu@xxxxxxxxx>

When enumerating xstate offsets and sizes from cpuid (eax=0x0d, ecx>=2),
it's possible that state m is not implemented while state n (n>m)
is implemented. So enumeration shouldn't stop at state m.

There is no platform configured like above yet. But this could be a problem
in the future. For example, suppose XCR0=0xe7, that means FP, SSE, AVX, and
AVX-512 states are enabled and MPX states (bit 3 and 4) are not enabled.
Then in setup_xstate_features(), after finding BNDREGS size is 0 (i.e. eax
from CPUID xstate subleaf 3, break from the for loop. That stops finding
xstate_offsets and xstate_sizes for AVX-512. Later on incorrect
xstate_offsets and xstate_sizes for AVX-512 will be used in a few places
and will causes issues.

This patch enumerates xstate offsets and sizes for all kernel supported
xstates. If a state is not implemented in hardware or not enabled in XCR0,
its size is set as zero and its offset is read from cpuid.

Ingo is rewriting fpu/xstate and his big patchset includes this patch at:
https://lkml.org/lkml/2015/5/5/892

I still send this patch in the patchset because we need to fix this bug
in upstream ASAP.

Signed-off-by: Fenghua Yu <fenghua.yu@xxxxxxxxx>
Reviewed-by: Dave Hansen <dave.hansen@xxxxxxxxx>
---
 arch/x86/kernel/xsave.c | 11 +++--------
 1 file changed, 3 insertions(+), 8 deletions(-)

diff --git a/arch/x86/kernel/xsave.c b/arch/x86/kernel/xsave.c
index 87a815b..3c0a9d1 100644
--- a/arch/x86/kernel/xsave.c
+++ b/arch/x86/kernel/xsave.c
@@ -465,23 +465,18 @@ static inline void xstate_enable(void)
  */
 static void __init setup_xstate_features(void)
 {
-	int eax, ebx, ecx, edx, leaf = 0x2;
+	int eax, ebx, ecx, edx, leaf;
 
 	xstate_features = fls64(pcntxt_mask);
 	xstate_offsets = alloc_bootmem(xstate_features * sizeof(int));
 	xstate_sizes = alloc_bootmem(xstate_features * sizeof(int));
 
-	do {
+	for (leaf = 2; leaf < xstate_features; leaf++) {
 		cpuid_count(XSTATE_CPUID, leaf, &eax, &ebx, &ecx, &edx);
 
-		if (eax == 0)
-			break;
-
 		xstate_offsets[leaf] = ebx;
 		xstate_sizes[leaf] = eax;
-
-		leaf++;
-	} while (1);
+	}
 }
 
 /*
-- 
1.8.1.2

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