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SubjectRe: [PATCH 1/3] x86/fpu/xstate: Fix last_good_offset in setup_xstate_features()
On Thu, Jan 09, 2020 at 01:14:50PM -0800, Yu-cheng Yu wrote:
> The function setup_xstate_features() uses CPUID to find each xfeature's
> standard-format offset and size. Since XSAVES always uses the compacted
> format, supervisor xstates are *NEVER* in the standard-format and their
> offsets are left as -1's. However, they are still being tracked as
> last_good_offset.
>
> Fix it by tracking only user xstate offsets.
>
> Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
> Reviewed-by: Dave Hansen <dave.hansen@linux.intel.com>
> ---
> arch/x86/kernel/fpu/xstate.c | 24 ++++++++++++++----------
> 1 file changed, 14 insertions(+), 10 deletions(-)

How about cleaning it up some more, while at it?

---
From c12e13dcd814023a903399ec5ac2e7082d664b8b Mon Sep 17 00:00:00 2001
From: Yu-cheng Yu <yu-cheng.yu@intel.com>
Date: Thu, 9 Jan 2020 13:14:50 -0800
Subject: [PATCH] x86/fpu/xstate: Fix last_good_offset in
setup_xstate_features()

The function setup_xstate_features() uses CPUID to find each xfeature's
standard-format offset and size. Since XSAVES always uses the compacted
format, supervisor xstates are *NEVER* in the standard-format and their
offsets are left as -1's. However, they are still being tracked as
last_good_offset.

Fix it by tracking only user xstate offsets.

[ bp: Use xfeature_is_supervisor() and save an indentation level. Drop
now unused xfeature_is_user(). ]

Signed-off-by: Yu-cheng Yu <yu-cheng.yu@intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Dave Hansen <dave.hansen@linux.intel.com>
Link: https://lkml.kernel.org/r/20200109211452.27369-2-yu-cheng.yu@intel.com
---
arch/x86/kernel/fpu/xstate.c | 27 +++++++++++++--------------
1 file changed, 13 insertions(+), 14 deletions(-)

diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
index a1806598aaa4..fe67cabfb4a1 100644
--- a/arch/x86/kernel/fpu/xstate.c
+++ b/arch/x86/kernel/fpu/xstate.c
@@ -120,11 +120,6 @@ static bool xfeature_is_supervisor(int xfeature_nr)
return ecx & 1;
}

-static bool xfeature_is_user(int xfeature_nr)
-{
- return !xfeature_is_supervisor(xfeature_nr);
-}
-
/*
* When executing XSAVEOPT (or other optimized XSAVE instructions), if
* a processor implementation detects that an FPU state component is still
@@ -265,21 +260,25 @@ static void __init setup_xstate_features(void)

cpuid_count(XSTATE_CPUID, i, &eax, &ebx, &ecx, &edx);

+ xstate_sizes[i] = eax;
+
/*
- * If an xfeature is supervisor state, the offset
- * in EBX is invalid. We leave it to -1.
+ * If an xfeature is supervisor state, the offset in EBX is
+ * invalid, leave it to -1.
*/
- if (xfeature_is_user(i))
- xstate_offsets[i] = ebx;
+ if (xfeature_is_supervisor(i))
+ continue;
+
+ xstate_offsets[i] = ebx;

- xstate_sizes[i] = eax;
/*
- * In our xstate size checks, we assume that the
- * highest-numbered xstate feature has the
- * highest offset in the buffer. Ensure it does.
+ * In our xstate size checks, we assume that the highest-numbered
+ * xstate feature has the highest offset in the buffer. Ensure
+ * it does.
*/
WARN_ONCE(last_good_offset > xstate_offsets[i],
- "x86/fpu: misordered xstate at %d\n", last_good_offset);
+ "x86/fpu: misordered xstate at %d\n", last_good_offset);
+
last_good_offset = xstate_offsets[i];
}
}
--
2.21.0
--
Regards/Gruss,
Boris.

https://people.kernel.org/tglx/notes-about-netiquette

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