Commit-ID: 85fb989d3a58cb9c7904bb7dd8264be61e18b185
Gitweb: http://git.kernel.org/tip/85fb989d3a58cb9c7904bb7dd8264be61e18b185
Author: Rik van Riel <riel@xxxxxxxxxx>
AuthorDate: Fri, 10 Feb 2017 08:54:45 -0500
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Sat, 11 Feb 2017 11:00:22 +0100
x86/fpu: Add FPU state copying quirk to handle XRSTOR failure on Intel Skylake CPUs
On Skylake CPUs I noticed that XRSTOR is unable to deal with states
created by copyout_from_xsaves() if the xstate has only SSE/YMM state, and
no FP state. That is, xfeatures had XFEATURE_MASK_SSE set, but not
XFEATURE_MASK_FP.
The reason is that part of the SSE/YMM state lives in the MXCSR and
MXCSR_FLAGS fields of the FP state.
Ensure that whenever we copy SSE or YMM state around, the MXCSR and
MXCSR_FLAGS fields are also copied around.
Signed-off-by: Rik van Riel <riel@xxxxxxxxxx>
Cc: Andy Lutomirski <luto@xxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxx>
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>
Cc: Yu-cheng Yu <yu-cheng.yu@xxxxxxxxx>
Link: http://lkml.kernel.org/r/20170210085445.0f1cc708@xxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
arch/x86/include/asm/fpu/types.h | 3 +++
arch/x86/kernel/fpu/xstate.c | 42 ++++++++++++++++++++++++++++++++++++++++
2 files changed, 45 insertions(+)
diff --git a/arch/x86/include/asm/fpu/types.h b/arch/x86/include/asm/fpu/types.h
index d15cbfe..ea65ab2 100644
--- a/arch/x86/include/asm/fpu/types.h
+++ b/arch/x86/include/asm/fpu/types.h
@@ -68,6 +68,9 @@ struct fxregs_state {
/* Default value for fxregs_state.mxcsr: */
#define MXCSR_DEFAULT 0x1f80
+/* Copy both mxcsr & mxcsr_flags with a single u64 memcpy: */
+#define MXCSR_AND_FLAGS_SIZE sizeof(u64)
+
/*
* Software based FPU emulation state. This is arbitrary really,
* it matches the x87 format to make it easier to understand:
diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c
index 772a069..2e89383 100644
--- a/arch/x86/kernel/fpu/xstate.c
+++ b/arch/x86/kernel/fpu/xstate.c
@@ -920,6 +920,23 @@ int arch_set_user_pkey_access(struct task_struct *tsk, int pkey,
#endif /* ! CONFIG_ARCH_HAS_PKEYS */
/*
+ * Weird legacy quirk: SSE and YMM states store information in the
+ * MXCSR and MXCSR_FLAGS fields of the FP area. That means if the FP
+ * area is marked as unused in the xfeatures header, we need to copy
+ * MXCSR and MXCSR_FLAGS if either SSE or YMM are in use.
+ */
+static inline bool xfeatures_mxcsr_quirk(u64 xfeatures)
+{
+ if (!(xfeatures & (XFEATURE_MASK_SSE|XFEATURE_MASK_YMM)))
+ return 0;
+
+ if (xfeatures & XFEATURE_MASK_FP)
+ return 0;
+
+ return 1;
+}
+
+/*
* This is similar to user_regset_copyout(), but will not add offset to
* the source data pointer or increment pos, count, kbuf, and ubuf.
*/
@@ -987,6 +1004,12 @@ int copy_xstate_to_kernel(void *kbuf, struct xregs_state *xsave, unsigned int of
}
+ if (xfeatures_mxcsr_quirk(header.xfeatures)) {
+ offset = offsetof(struct fxregs_state, mxcsr);
+ size = MXCSR_AND_FLAGS_SIZE;
+ __copy_xstate_to_kernel(kbuf, &xsave->i387.mxcsr, offset, size, size_total);
+ }
+
/*
* Fill xsave->i387.sw_reserved value for ptrace frame:
*/
@@ -1069,6 +1092,12 @@ int copy_xstate_to_user(void __user *ubuf, struct xregs_state *xsave, unsigned i
}
+ if (xfeatures_mxcsr_quirk(header.xfeatures)) {
+ offset = offsetof(struct fxregs_state, mxcsr);
+ size = MXCSR_AND_FLAGS_SIZE;
+ __copy_xstate_to_user(ubuf, &xsave->i387.mxcsr, offset, size, size_total);
+ }
+
/*
* Fill xsave->i387.sw_reserved value for ptrace frame:
*/
@@ -1121,6 +1150,12 @@ int copy_kernel_to_xstate(struct xregs_state *xsave, const void *kbuf)
}
}
+ if (xfeatures_mxcsr_quirk(xfeatures)) {
+ offset = offsetof(struct fxregs_state, mxcsr);
+ size = MXCSR_AND_FLAGS_SIZE;
+ memcpy(&xsave->i387.mxcsr, kbuf + offset, size);
+ }
+
/*
* The state that came in from userspace was user-state only.
* Mask all the user states out of 'xfeatures':
@@ -1176,6 +1211,13 @@ int copy_user_to_xstate(struct xregs_state *xsave, const void __user *ubuf)
}
}
+ if (xfeatures_mxcsr_quirk(xfeatures)) {
+ offset = offsetof(struct fxregs_state, mxcsr);
+ size = MXCSR_AND_FLAGS_SIZE;
+ if (__copy_from_user(&xsave->i387.mxcsr, ubuf + offset, size))
+ return -EFAULT;
+ }
+
/*
* The state that came in from userspace was user-state only.
* Mask all the user states out of 'xfeatures':
--
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