Messages in this thread | | | From | "Chang S. Bae" <> | Subject | [PATCH 0/1] x86/fpu: Follow up on the init_fpstate fix | Date | Tue, 18 Oct 2022 15:13:48 -0700 |
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In short, the init_fpstate fix currently at tip's x86/urgent [6] is incomplete for KVM. This patch follows up on that.
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While these patches [1][2] attempt to fix the init fpstate, it results in a fallout with KVM [3]:
The VCPU's XSAVE buffer is expanded at the time of VCPU setup [4] when any dynamic feature is determined to be exposed via KVM_SET_CPUID.
Then, when the VCPU thread is executed [5], the xstate is copied to the userspace via KVM_GET_XSAVE*. At the moment, the entire guest fpstate is in init state.
But, init_fpstate has been incorrectly indicating the inclusion of dynamic states. Subsequently, in the xstate copy loop, memory beyond the init_fpstate looks to be referenced for the init states of dynamic features.
The tip-merged series [1] fixes init_fpstate only. The xstate copy loop remains to retrieve init_fpstate. Then, it will explode when a dynamic-featured VCPU is about executed.
The included patch is to fix the copy function. It is based on the x86/urgent branch [6].
Thanks, Chang
[1] https://lore.kernel.org/lkml/20220824191223.1248-1-chang.seok.bae@intel.com/ [2] https://lore.kernel.org/lkml/20221011222425.866137-1-dave.hansen@linux.intel.com/ [3] https://lore.kernel.org/lkml/BYAPR11MB3717EDEF2351C958F2C86EED95259@BYAPR11MB3717.namprd11.prod.outlook.com/ [4] https://gitlab.com/qemu-project/qemu/-/blob/master/accel/kvm/kvm-accel-ops.c#L42 [5] https://gitlab.com/qemu-project/qemu/-/blob/master/accel/kvm/kvm-accel-ops.c#L51 [6] https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git/log/?h=x86/urgent
Chang S. Bae (1): x86/fpu: Fix copy_xstate_to_uabi() to copy init states correctly
arch/x86/kernel/fpu/xstate.c | 10 +++++++--- 1 file changed, 7 insertions(+), 3 deletions(-)
base-commit: 67bf6493449b09590f9f71d7df29efb392b12d25 -- 2.17.1
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