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SubjectRe: [PATCH v2 0/5] KVM: VMX: Optimize VMX instrs error/fault handling
Paolo,

Any chance this can be picked up for 5.4? Josh's kvm_spurious_fault()
changes went into 5.3, so this can be taken through the KVM tree, which
probably makes the most sense since the non-KVM change is a one line
deletion.

On Fri, Jul 19, 2019 at 01:41:05PM -0700, Sean Christopherson wrote:
> A recent commit reworked __kvm_handle_fault_on_reboot() to play nice with
> objtool. An unfortunate side effect is that JMP is now inserted after
> most VMX instructions so that the reboot macro can use an actual CALL to
> kvm_spurious_fault() instead of a funky PUSH+JMP facsimile in .fixup.
>
> Rework the low level VMX instruction helpers to handle unexpected faults
> manually instead of relying on the "fault on reboot" macro. By using
> asm-goto, most helpers can branch directly to an in-function call to
> kvm_spurious_fault(), which can then be optimized by compilers to reside
> out-of-line at the end of the function instead of inline as done by
> "fault on reboot".
>
> The net impact relative to the current code base is more or less a nop
> when building with a compiler that supports __GCC_ASM_FLAG_OUTPUTS__.
> A bunch of code that was previously in .fixup gets moved into the slow
> paths of functions, but the fast paths are more basically unchanged.
>
> Without __GCC_ASM_FLAG_OUTPUTS__, manually coding the Jcc is a net
> positive as CC_SET() without compiler support almost always generates a
> SETcc+CMP+Jcc sequence, which is now replaced with a single Jcc.
>
> A small bonus is that the Jcc instrs are hinted to predict that the VMX
> instr will be successful.
>
> v2:
> - Rebased to x86/master, commit eceffd88ca20 ("Merge branch 'x86/urgent'")
> - Reworded changelogs to reference the commit instead lkml link for
> the recent changes to __kvm_handle_fault_on_reboot().
> - Added Paolo's acks for patch 1-4
> - Added patch 5 to do more cleanup, which was made possible by rebasing
> on top of the __kvm_handle_fault_on_reboot() changes.
>
> Sean Christopherson (5):
> objtool: KVM: x86: Check kvm_rebooting in kvm_spurious_fault()
> KVM: VMX: Optimize VMX instruction error and fault handling
> KVM: VMX: Add error handling to VMREAD helper
> KVM: x86: Drop ____kvm_handle_fault_on_reboot()
> KVM: x86: Don't check kvm_rebooting in __kvm_handle_fault_on_reboot()
>
> arch/x86/include/asm/kvm_host.h | 16 ++----
> arch/x86/kvm/vmx/ops.h | 93 ++++++++++++++++++++-------------
> arch/x86/kvm/vmx/vmx.c | 42 +++++++++++++++
> arch/x86/kvm/x86.c | 3 +-
> tools/objtool/check.c | 1 -
> 5 files changed, 104 insertions(+), 51 deletions(-)
>
> --
> 2.22.0
>

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