The following commit has been merged into the x86/fpu branch of tip:
Commit-ID: c351101678ce54492b6e09810ec02efc0df036a9
Gitweb: https://git.kernel.org/tip/c351101678ce54492b6e09810ec02efc0df036a9
Author: Chang S. Bae <chang.seok.bae@xxxxxxxxx>
AuthorDate: Thu, 21 Oct 2021 15:55:16 -07:00
Committer: Borislav Petkov <bp@xxxxxxx>
CommitterDate: Tue, 26 Oct 2021 10:18:09 +02:00
x86/cpufeatures: Add eXtended Feature Disabling (XFD) feature bit
Intel's eXtended Feature Disable (XFD) feature is an extension of the XSAVE
architecture. XFD allows the kernel to enable a feature state in XCR0 and
to receive a #NM trap when a task uses instructions accessing that state.
This is going to be used to postpone the allocation of a larger XSTATE
buffer for a task to the point where it is actually using a related
instruction after the permission to use that facility has been granted.
XFD is not used by the kernel, but only applied to userspace. This is a
matter of policy as the kernel knows how a fpstate is reallocated and the
XFD state.
The compacted XSAVE format is adjustable for dynamic features. Make XFD
depend on XSAVES.
Signed-off-by: Chang S. Bae <chang.seok.bae@xxxxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Chang S. Bae <chang.seok.bae@xxxxxxxxx>
Signed-off-by: Borislav Petkov <bp@xxxxxxx>
Link: https://lkml.kernel.org/r/20211021225527.10184-13-chang.seok.bae@xxxxxxxxx
---
arch/x86/include/asm/cpufeatures.h | 1 +
arch/x86/kernel/cpu/cpuid-deps.c | 1 +
2 files changed, 2 insertions(+)
diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
index d0ce5cf..ab7b3a2 100644
--- a/arch/x86/include/asm/cpufeatures.h
+++ b/arch/x86/include/asm/cpufeatures.h
@@ -277,6 +277,7 @@
#define X86_FEATURE_XSAVEC (10*32+ 1) /* XSAVEC instruction */
#define X86_FEATURE_XGETBV1 (10*32+ 2) /* XGETBV with ECX = 1 instruction */
#define X86_FEATURE_XSAVES (10*32+ 3) /* XSAVES/XRSTORS instructions */
+#define X86_FEATURE_XFD (10*32+ 4) /* "" eXtended Feature Disabling */
/*
* Extended auxiliary flags: Linux defined - for features scattered in various
diff --git a/arch/x86/kernel/cpu/cpuid-deps.c b/arch/x86/kernel/cpu/cpuid-deps.c
index defda61..d9ead9c 100644
--- a/arch/x86/kernel/cpu/cpuid-deps.c
+++ b/arch/x86/kernel/cpu/cpuid-deps.c
@@ -75,6 +75,7 @@ static const struct cpuid_dep cpuid_deps[] = {
{ X86_FEATURE_SGX_LC, X86_FEATURE_SGX },
{ X86_FEATURE_SGX1, X86_FEATURE_SGX },
{ X86_FEATURE_SGX2, X86_FEATURE_SGX1 },
+ { X86_FEATURE_XFD, X86_FEATURE_XSAVES },
{}
};
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