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SubjectRe: [PATCH 1/2] KVM: X86: Single target IPI fastpath
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Ok, it's not _so_ ugly after all.

> ---
> arch/x86/kvm/vmx/vmx.c | 39 +++++++++++++++++++++++++++++++++++++--
> include/linux/kvm_host.h | 1 +
> 2 files changed, 38 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 5d21a4a..5c67061 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -5924,7 +5924,9 @@ static int vmx_handle_exit(struct kvm_vcpu *vcpu)
> }
> }
>
> - if (exit_reason < kvm_vmx_max_exit_handlers
> + if (vcpu->fast_vmexit)
> + return 1;
> + else if (exit_reason < kvm_vmx_max_exit_handlers

Instead of a separate vcpu->fast_vmexit, perhaps you can set exit_reason
to vmx->exit_reason to -1 if the fast path succeeds.

> + if (ret == 0)
> + ret = kvm_skip_emulated_instruction(vcpu);

Please move the "kvm_skip_emulated_instruction(vcpu)" to
vmx_handle_exit, so that this basically is

#define EXIT_REASON_NEED_SKIP_EMULATED_INSN -1

if (ret == 0)
vcpu->exit_reason = EXIT_REASON_NEED_SKIP_EMULATED_INSN;

and handle_ipi_fastpath can return void.

Thanks,

Paolo

> + };
> + };
> +
> + return ret;
> +}
> +
> static void vmx_vcpu_run(struct kvm_vcpu *vcpu)
> {
> struct vcpu_vmx *vmx = to_vmx(vcpu);
> @@ -6615,6 +6645,12 @@ static void vmx_vcpu_run(struct kvm_vcpu *vcpu)
> | (1 << VCPU_EXREG_CR3));
> vcpu->arch.regs_dirty = 0;
>
> + vmx->exit_reason = vmx->fail ? 0xdead : vmcs_read32(VM_EXIT_REASON);
> + vcpu->fast_vmexit = false;
> + if (!is_guest_mode(vcpu) &&
> + vmx->exit_reason == EXIT_REASON_MSR_WRITE)
> + vcpu->fast_vmexit = handle_ipi_fastpath(vcpu);

This should be done later, at least after kvm_put_guest_xcr0, because
running with partially-loaded guest state is harder to audit. The best
place to put it actually is right after the existing vmx->exit_reason
assignment, where we already handle EXIT_REASON_MCE_DURING_VMENTRY.

> pt_guest_exit(vmx);
>
> /*
> @@ -6634,7 +6670,6 @@ static void vmx_vcpu_run(struct kvm_vcpu *vcpu)
> vmx->nested.nested_run_pending = 0;
> vmx->idt_vectoring_info = 0;
>
> - vmx->exit_reason = vmx->fail ? 0xdead : vmcs_read32(VM_EXIT_REASON);
> if ((u16)vmx->exit_reason == EXIT_REASON_MCE_DURING_VMENTRY)
> kvm_machine_check();
>
> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> index 719fc3e..7a7358b 100644
> --- a/include/linux/kvm_host.h
> +++ b/include/linux/kvm_host.h
> @@ -319,6 +319,7 @@ struct kvm_vcpu {
> #endif
> bool preempted;
> bool ready;
> + bool fast_vmexit;
> struct kvm_vcpu_arch arch;
> struct dentry *debugfs_dentry;
> };
>

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