Messages in this thread Patch in this message | | | From | riel@redhat ... | Subject | [PATCH 2/2] x86/fpu: copy MXCSR & MXCSR_FLAGS with SSE/YMM state | Date | Wed, 25 Jan 2017 20:57:59 -0500 |
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From: Rik van Riel <riel@redhat.com>
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@redhat.com> --- arch/x86/kernel/fpu/xstate.c | 39 ++++++++++++++++++++++++++++++++++++++- 1 file changed, 38 insertions(+), 1 deletion(-)
diff --git a/arch/x86/kernel/fpu/xstate.c b/arch/x86/kernel/fpu/xstate.c index c1508d56ecfb..10b10917af81 100644 --- a/arch/x86/kernel/fpu/xstate.c +++ b/arch/x86/kernel/fpu/xstate.c @@ -1004,6 +1004,23 @@ int copyout_from_xsaves(unsigned int pos, unsigned int count, void *kbuf, } /* + * Restoring SSE/YMM state requires that MXCSR & MXCSR_MASK are saved. + * Those fields are part of the legacy FP state, and only get saved + * above if XFEATURES_MASK_FP is set. + * + * Copy out those fields if we have SSE/YMM but no FP register data. + */ + if ((header.xfeatures & (XFEATURE_MASK_SSE|XFEATURE_MASK_YMM)) && + !(header.xfeatures & XFEATURE_MASK_FP)) { + size = sizeof(u64); + ret = xstate_copyout(offset, size, kbuf, ubuf, + &xsave->i387.mxcsr, 0, count); + + if (ret) + return ret; + } + + /* * Fill xsave->i387.sw_reserved value for ptrace frame: */ offset = offsetof(struct fxregs_state, sw_reserved); @@ -1030,6 +1047,7 @@ int copyin_to_xsaves(const void *kbuf, const void __user *ubuf, int i; u64 xfeatures; u64 allowed_features; + void *dst; offset = offsetof(struct xregs_state, header); size = sizeof(xfeatures); @@ -1053,7 +1071,7 @@ int copyin_to_xsaves(const void *kbuf, const void __user *ubuf, u64 mask = ((u64)1 << i); if (xfeatures & mask) { - void *dst = __raw_xsave_addr(xsave, 1 << i); + dst = __raw_xsave_addr(xsave, 1 << i); offset = xstate_offsets[i]; size = xstate_sizes[i]; @@ -1068,6 +1086,25 @@ int copyin_to_xsaves(const void *kbuf, const void __user *ubuf, } /* + * SSE/YMM state depends on the MXCSR & MXCSR_MASK fields from the FP + * state. If we restored only SSE/YMM state but not FP state, copy + * those fields to ensure the SSE/YMM state restore works. + */ + if ((xfeatures & (XFEATURE_MASK_SSE|XFEATURE_MASK_YMM)) && + !(xfeatures & XFEATURE_MASK_FP)) { + offset = offsetof(struct fxregs_state, mxcsr); + dst = xsave + offset; + size = sizeof(u64); + + if (kbuf) { + memcpy(dst, kbuf + offset, size); + } else { + if (__copy_from_user(dst, ubuf + offset, size)) + return -EFAULT; + } + } + + /* * The state that came in from userspace was user-state only. * Mask all the user states out of 'xfeatures': */ -- 2.9.3
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