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Date: Wed, 22 Dec 2021 15:25:32 +0100
From: Paolo Bonzini <pbonzini@...hat.com>
To: Michael Roth <michael.roth@....com>,
linux-kselftest@...r.kernel.org
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org, x86@...nel.org,
Nathan Tempelman <natet@...gle.com>,
Marc Orr <marcorr@...gle.com>,
Steve Rutherford <srutherford@...gle.com>,
Sean Christopherson <seanjc@...gle.com>,
Mingwei Zhang <mizhang@...gle.com>,
Brijesh Singh <brijesh.singh@....com>,
Tom Lendacky <thomas.lendacky@....com>,
Varad Gautam <varad.gautam@...e.com>,
Shuah Khan <shuah@...nel.org>,
Vitaly Kuznetsov <vkuznets@...hat.com>,
David Woodhouse <dwmw@...zon.co.uk>,
Ricardo Koller <ricarkol@...gle.com>,
Jim Mattson <jmattson@...gle.com>,
Joerg Roedel <joro@...tes.org>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
"H . Peter Anvin" <hpa@...or.com>,
Krish Sadhukhan <krish.sadhukhan@...cle.com>,
Peter Gonda <pgonda@...gle.com>
Subject: Re: [PATCH v2 09/13] KVM: SVM: include CR3 in initial VMSA state for
SEV-ES guests
On 12/16/21 18:13, Michael Roth wrote:
> Normally guests will set up CR3 themselves, but some guests, such as
> kselftests, and potentially CONFIG_PVH guests, rely on being booted
> with paging enabled and CR3 initialized to a pre-allocated page table.
>
> Currently CR3 updates via KVM_SET_SREGS* are not loaded into the guest
> VMCB until just prior to entering the guest. For SEV-ES/SEV-SNP, this
> is too late, since it will have switched over to using the VMSA page
> prior to that point, with the VMSA CR3 copied from the VMCB initial
> CR3 value: 0.
>
> Address this by sync'ing the CR3 value into the VMCB save area
> immediately when KVM_SET_SREGS* is issued so it will find it's way into
> the initial VMSA.
>
> Suggested-by: Tom Lendacky <thomas.lendacky@....com>
> Signed-off-by: Michael Roth <michael.roth@....com>
> ---
> arch/x86/include/asm/kvm-x86-ops.h | 1 +
> arch/x86/include/asm/kvm_host.h | 1 +
> arch/x86/kvm/svm/svm.c | 19 +++++++++++++++++++
> arch/x86/kvm/vmx/vmx.c | 6 ++++++
> arch/x86/kvm/x86.c | 1 +
> 5 files changed, 28 insertions(+)
>
> diff --git a/arch/x86/include/asm/kvm-x86-ops.h b/arch/x86/include/asm/kvm-x86-ops.h
> index cefe1d81e2e8..a3172bd59690 100644
> --- a/arch/x86/include/asm/kvm-x86-ops.h
> +++ b/arch/x86/include/asm/kvm-x86-ops.h
> @@ -35,6 +35,7 @@ KVM_X86_OP(get_cpl)
> KVM_X86_OP(set_segment)
> KVM_X86_OP_NULL(get_cs_db_l_bits)
> KVM_X86_OP(set_cr0)
> +KVM_X86_OP(post_set_cr3)
> KVM_X86_OP(is_valid_cr4)
> KVM_X86_OP(set_cr4)
> KVM_X86_OP(set_efer)
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index d5fede05eb5f..22f384320ed1 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -1342,6 +1342,7 @@ struct kvm_x86_ops {
> struct kvm_segment *var, int seg);
> void (*get_cs_db_l_bits)(struct kvm_vcpu *vcpu, int *db, int *l);
> void (*set_cr0)(struct kvm_vcpu *vcpu, unsigned long cr0);
> + void (*post_set_cr3)(struct kvm_vcpu *vcpu, unsigned long cr3);
> bool (*is_valid_cr4)(struct kvm_vcpu *vcpu, unsigned long cr0);
> void (*set_cr4)(struct kvm_vcpu *vcpu, unsigned long cr4);
> int (*set_efer)(struct kvm_vcpu *vcpu, u64 efer);
> diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
> index 208566f63bce..76e906d83a84 100644
> --- a/arch/x86/kvm/svm/svm.c
> +++ b/arch/x86/kvm/svm/svm.c
> @@ -1792,6 +1792,24 @@ static void svm_set_gdt(struct kvm_vcpu *vcpu, struct desc_ptr *dt)
> vmcb_mark_dirty(svm->vmcb, VMCB_DT);
> }
>
> +static void svm_post_set_cr3(struct kvm_vcpu *vcpu, unsigned long cr3)
> +{
> + struct vcpu_svm *svm = to_svm(vcpu);
> +
> + /*
> + * For guests that don't set guest_state_protected, the cr3 update is
> + * handled via kvm_mmu_load() while entering the guest. For guests
> + * that do (SEV-ES/SEV-SNP), the cr3 update needs to be written to
> + * VMCB save area now, since the save area will become the initial
> + * contents of the VMSA, and future VMCB save area updates won't be
> + * seen.
> + */
> + if (sev_es_guest(vcpu->kvm)) {
> + svm->vmcb->save.cr3 = cr3;
> + vmcb_mark_dirty(svm->vmcb, VMCB_CR);
> + }
> +}
> +
> void svm_set_cr0(struct kvm_vcpu *vcpu, unsigned long cr0)
> {
> struct vcpu_svm *svm = to_svm(vcpu);
> @@ -4622,6 +4640,7 @@ static struct kvm_x86_ops svm_x86_ops __initdata = {
> .get_cpl = svm_get_cpl,
> .get_cs_db_l_bits = kvm_get_cs_db_l_bits,
> .set_cr0 = svm_set_cr0,
> + .post_set_cr3 = svm_post_set_cr3,
> .is_valid_cr4 = svm_is_valid_cr4,
> .set_cr4 = svm_set_cr4,
> .set_efer = svm_set_efer,
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 63615d242bdf..075107c1b3f5 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -3124,6 +3124,11 @@ static void vmx_load_mmu_pgd(struct kvm_vcpu *vcpu, hpa_t root_hpa,
> vmcs_writel(GUEST_CR3, guest_cr3);
> }
>
> +
> +void vmx_post_set_cr3(struct kvm_vcpu *vcpu, unsigned long cr3)
> +{
> +}
> +
> static bool vmx_is_valid_cr4(struct kvm_vcpu *vcpu, unsigned long cr4)
> {
> /*
> @@ -7597,6 +7602,7 @@ static struct kvm_x86_ops vmx_x86_ops __initdata = {
> .get_cpl = vmx_get_cpl,
> .get_cs_db_l_bits = vmx_get_cs_db_l_bits,
> .set_cr0 = vmx_set_cr0,
> + .post_set_cr3 = vmx_post_set_cr3,
> .is_valid_cr4 = vmx_is_valid_cr4,
> .set_cr4 = vmx_set_cr4,
> .set_efer = vmx_set_efer,
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 26cb3a4cd0e9..c0d84a4c8049 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -10609,6 +10609,7 @@ static int __set_sregs_common(struct kvm_vcpu *vcpu, struct kvm_sregs *sregs,
> *mmu_reset_needed |= kvm_read_cr3(vcpu) != sregs->cr3;
> vcpu->arch.cr3 = sregs->cr3;
> kvm_register_mark_dirty(vcpu, VCPU_EXREG_CR3);
> + static_call(kvm_x86_post_set_cr3)(vcpu, sregs->cr3);
>
> kvm_set_cr8(vcpu, sregs->cr8);
>
>
I'm going to apply this one now, just with a small change to avoid
vmx_post_set_cr3 and a remark about why kvm_set_cr3 is not calling the
new hook.
diff --git a/arch/x86/include/asm/kvm-x86-ops.h
b/arch/x86/include/asm/kvm-x86-ops.h
index 8803773539a0..37624a9e3e40 100644
--- a/arch/x86/include/asm/kvm-x86-ops.h
+++ b/arch/x86/include/asm/kvm-x86-ops.h
@@ -35,7 +35,7 @@ KVM_X86_OP(get_cpl)
KVM_X86_OP(set_segment)
KVM_X86_OP_NULL(get_cs_db_l_bits)
KVM_X86_OP(set_cr0)
-KVM_X86_OP(post_set_cr3)
+KVM_X86_OP_NULL(post_set_cr3)
KVM_X86_OP(is_valid_cr4)
KVM_X86_OP(set_cr4)
KVM_X86_OP(set_efer)
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index a39da103e33c..fe06b02994e6 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -3135,10 +3135,6 @@ static void vmx_load_mmu_pgd(struct kvm_vcpu
*vcpu, hpa_t root_hpa,
}
-void vmx_post_set_cr3(struct kvm_vcpu *vcpu, unsigned long cr3)
-{
-}
-
static bool vmx_is_valid_cr4(struct kvm_vcpu *vcpu, unsigned long cr4)
{
/*
@@ -7608,7 +7604,6 @@ static struct kvm_x86_ops vmx_x86_ops __initdata = {
.get_cpl = vmx_get_cpl,
.get_cs_db_l_bits = vmx_get_cs_db_l_bits,
.set_cr0 = vmx_set_cr0,
- .post_set_cr3 = vmx_post_set_cr3,
.is_valid_cr4 = vmx_is_valid_cr4,
.set_cr4 = vmx_set_cr4,
.set_efer = vmx_set_efer,
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index db118066c653..c194a8cbd25f 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1179,6 +1179,7 @@ int kvm_set_cr3(struct kvm_vcpu *vcpu, unsigned
long cr3)
vcpu->arch.cr3 = cr3;
kvm_register_mark_dirty(vcpu, VCPU_EXREG_CR3);
+ /* Do not call post_set_cr3, we do not get here for confidential
guests. */
handle_tlb_flush:
/*
@@ -10636,7 +10637,7 @@ static int __set_sregs_common(struct kvm_vcpu
*vcpu, struct kvm_sregs *sregs,
*mmu_reset_needed |= kvm_read_cr3(vcpu) != sregs->cr3;
vcpu->arch.cr3 = sregs->cr3;
kvm_register_mark_dirty(vcpu, VCPU_EXREG_CR3);
- static_call(kvm_x86_post_set_cr3)(vcpu, sregs->cr3);
+ static_call_cond(kvm_x86_post_set_cr3)(vcpu, sregs->cr3);
kvm_set_cr8(vcpu, sregs->cr8);
Paolo
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