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SubjectRe: [RFC PATCH 22/35] KVM: SVM: Add support for CR0 write traps for an SEV-ES guest
On Mon, Sep 14, 2020 at 03:15:36PM -0500, Tom Lendacky wrote:
> From: Tom Lendacky <thomas.lendacky@amd.com>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index b65bd0c986d4..6f5988c305e1 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -799,11 +799,29 @@ bool pdptrs_changed(struct kvm_vcpu *vcpu)
> }
> EXPORT_SYMBOL_GPL(pdptrs_changed);
>
> +static void kvm_post_set_cr0(struct kvm_vcpu *vcpu, unsigned long old_cr0,
> + unsigned long cr0)

What about using __kvm_set_cr*() instead of kvm_post_set_cr*()? That would
show that __kvm_set_cr*() is a subordinate of kvm_set_cr*(), and from the
SVM side would provide the hint that the code is skipping the front end of
kvm_set_cr*().

> +{
> + unsigned long update_bits = X86_CR0_PG | X86_CR0_WP;
> +
> + if ((cr0 ^ old_cr0) & X86_CR0_PG) {
> + kvm_clear_async_pf_completion_queue(vcpu);
> + kvm_async_pf_hash_reset(vcpu);
> + }
> +
> + if ((cr0 ^ old_cr0) & update_bits)
> + kvm_mmu_reset_context(vcpu);
> +
> + if (((cr0 ^ old_cr0) & X86_CR0_CD) &&
> + kvm_arch_has_noncoherent_dma(vcpu->kvm) &&
> + !kvm_check_has_quirk(vcpu->kvm, KVM_X86_QUIRK_CD_NW_CLEARED))
> + kvm_zap_gfn_range(vcpu->kvm, 0, ~0ULL);
> +}
> +
> int kvm_set_cr0(struct kvm_vcpu *vcpu, unsigned long cr0)
> {
> unsigned long old_cr0 = kvm_read_cr0(vcpu);
> unsigned long pdptr_bits = X86_CR0_CD | X86_CR0_NW | X86_CR0_PG;
> - unsigned long update_bits = X86_CR0_PG | X86_CR0_WP;
>
> cr0 |= X86_CR0_ET;
>
> @@ -842,22 +860,23 @@ int kvm_set_cr0(struct kvm_vcpu *vcpu, unsigned long cr0)
>
> kvm_x86_ops.set_cr0(vcpu, cr0);
>
> - if ((cr0 ^ old_cr0) & X86_CR0_PG) {
> - kvm_clear_async_pf_completion_queue(vcpu);
> - kvm_async_pf_hash_reset(vcpu);
> - }
> + kvm_post_set_cr0(vcpu, old_cr0, cr0);
>
> - if ((cr0 ^ old_cr0) & update_bits)
> - kvm_mmu_reset_context(vcpu);
> + return 0;
> +}
> +EXPORT_SYMBOL_GPL(kvm_set_cr0);
>
> - if (((cr0 ^ old_cr0) & X86_CR0_CD) &&
> - kvm_arch_has_noncoherent_dma(vcpu->kvm) &&
> - !kvm_check_has_quirk(vcpu->kvm, KVM_X86_QUIRK_CD_NW_CLEARED))
> - kvm_zap_gfn_range(vcpu->kvm, 0, ~0ULL);
> +int kvm_track_cr0(struct kvm_vcpu *vcpu, unsigned long cr0)

I really dislike the "track" terminology. For me, using "track" as the verb
in a function implies the function activates tracking. But it's probably a
moot point, because similar to EFER, I don't see any reason to put the front
end of the emulation into x86.c. Both getting old_cr0 and setting
vcpu->arch.cr0 can be done in svm.c

> +{
> + unsigned long old_cr0 = kvm_read_cr0(vcpu);
> +
> + vcpu->arch.cr0 = cr0;
> +
> + kvm_post_set_cr0(vcpu, old_cr0, cr0);
>
> return 0;
> }
> -EXPORT_SYMBOL_GPL(kvm_set_cr0);
> +EXPORT_SYMBOL_GPL(kvm_track_cr0);
>
> void kvm_lmsw(struct kvm_vcpu *vcpu, unsigned long msw)
> {
> --
> 2.28.0
>

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