On Sun, Sep 19, 2021, Lai Jiangshan wrote:
> From: Lai Jiangshan <laijs@xxxxxxxxxxxxxxxxx>
>
> X86_CR4_PCIDE doesn't participate in kvm_mmu_role, so the mmu context
> doesn't need to be reset. It is only required to flush all the guest
> tlb.
>
> Signed-off-by: Lai Jiangshan <laijs@xxxxxxxxxxxxxxxxx>
> ---
> arch/x86/kvm/x86.c | 6 ++++--
> 1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 86539c1686fa..7494ea0e7922 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -116,6 +116,7 @@ static void enter_smm(struct kvm_vcpu *vcpu);
> static void __kvm_set_rflags(struct kvm_vcpu *vcpu, unsigned long rflags);
> static void store_regs(struct kvm_vcpu *vcpu);
> static int sync_regs(struct kvm_vcpu *vcpu);
> +static void kvm_vcpu_flush_tlb_guest(struct kvm_vcpu *vcpu);
>
> static int __set_sregs2(struct kvm_vcpu *vcpu, struct kvm_sregs2 *sregs2);
> static void __get_sregs2(struct kvm_vcpu *vcpu, struct kvm_sregs2 *sregs2);
> @@ -1042,9 +1043,10 @@ EXPORT_SYMBOL_GPL(kvm_is_valid_cr4);
>
> void kvm_post_set_cr4(struct kvm_vcpu *vcpu, unsigned long old_cr4, unsigned long cr4)
> {
> - if (((cr4 ^ old_cr4) & KVM_MMU_CR4_ROLE_BITS) ||
> - (!(cr4 & X86_CR4_PCIDE) && (old_cr4 & X86_CR4_PCIDE)))
> + if ((cr4 ^ old_cr4) & KVM_MMU_CR4_ROLE_BITS)
> kvm_mmu_reset_context(vcpu);
> + else if (!(cr4 & X86_CR4_PCIDE) && (old_cr4 & X86_CR4_PCIDE))
> + kvm_vcpu_flush_tlb_guest(vcpu);
Unless there's a corner case I'm missing, I would prefer this to use
kvm_make_request(KVM_REQ_TLB_FLUSH_GUEST, vcpu) instead of calling
kvm_vcpu_flush_tlb_guest() directly. The odds of flushes actually being batched
is low, it's more to document that kvm_post_set_cr4() _isn't_ special.
