diff mbox series

[RFC,09/35] KVM: SVM: Do not emulate MMIO under SEV-ES

Message ID c4ccb48b41f3996bc9000730309455e449cb1136.1600114548.git.thomas.lendacky@amd.com (mailing list archive)
State New, archived
Headers show
Series SEV-ES hypervisor support | expand

Commit Message

Tom Lendacky Sept. 14, 2020, 8:15 p.m. UTC 
From: Tom Lendacky <thomas.lendacky@amd.com>

When a guest is running as an SEV-ES guest, it is not possible to emulate
MMIO. Add support to prevent trying to perform MMIO emulation.

Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
---
 arch/x86/kvm/mmu/mmu.c | 7 +++++++
 1 file changed, 7 insertions(+)

Comments

Sean Christopherson Sept. 14, 2020, 9:33 p.m. UTC | #1 
On Mon, Sep 14, 2020 at 03:15:23PM -0500, Tom Lendacky wrote:
> From: Tom Lendacky <thomas.lendacky@amd.com>
> 
> When a guest is running as an SEV-ES guest, it is not possible to emulate
> MMIO. Add support to prevent trying to perform MMIO emulation.
> 
> Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
> ---
>  arch/x86/kvm/mmu/mmu.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index a5d0207e7189..2e1b8b876286 100644
> --- a/arch/x86/kvm/mmu/mmu.c
> +++ b/arch/x86/kvm/mmu/mmu.c
> @@ -5485,6 +5485,13 @@ int kvm_mmu_page_fault(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa, u64 error_code,
>  	if (!mmio_info_in_cache(vcpu, cr2_or_gpa, direct) && !is_guest_mode(vcpu))
>  		emulation_type |= EMULTYPE_ALLOW_RETRY_PF;
>  emulate:
> +	/*
> +	 * When the guest is an SEV-ES guest, emulation is not possible.  Allow
> +	 * the guest to handle the MMIO emulation.
> +	 */
> +	if (vcpu->arch.vmsa_encrypted)
> +		return 1;

A better approach is to refactor need_emulation_on_page_fault() (the hook
that's just out of sight in this patch) into a more generic
kvm_x86_ops.is_emulatable() so that the latter can be used to kill emulation
everywhere, and for other reasons.  E.g. TDX obviously shares very similar
logic, but SGX also adds a case where KVM can theoretically end up in an
emulator path without the ability to access the necessary guest state.

I have exactly such a prep patch (because SGX and TDX...), I'll get it posted
in the next day or two.

> +
>  	/*
>  	 * On AMD platforms, under certain conditions insn_len may be zero on #NPF.
>  	 * This can happen if a guest gets a page-fault on data access but the HW
> -- 
> 2.28.0
>
Tom Lendacky Sept. 15, 2020, 1:38 p.m. UTC | #2 
On 9/14/20 4:33 PM, Sean Christopherson wrote:
> On Mon, Sep 14, 2020 at 03:15:23PM -0500, Tom Lendacky wrote:
>> From: Tom Lendacky <thomas.lendacky@amd.com>
>>
>> When a guest is running as an SEV-ES guest, it is not possible to emulate
>> MMIO. Add support to prevent trying to perform MMIO emulation.
>>
>> Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
>> ---
>>  arch/x86/kvm/mmu/mmu.c | 7 +++++++
>>  1 file changed, 7 insertions(+)
>>
>> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
>> index a5d0207e7189..2e1b8b876286 100644
>> --- a/arch/x86/kvm/mmu/mmu.c
>> +++ b/arch/x86/kvm/mmu/mmu.c
>> @@ -5485,6 +5485,13 @@ int kvm_mmu_page_fault(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa, u64 error_code,
>>  	if (!mmio_info_in_cache(vcpu, cr2_or_gpa, direct) && !is_guest_mode(vcpu))
>>  		emulation_type |= EMULTYPE_ALLOW_RETRY_PF;
>>  emulate:
>> +	/*
>> +	 * When the guest is an SEV-ES guest, emulation is not possible.  Allow
>> +	 * the guest to handle the MMIO emulation.
>> +	 */
>> +	if (vcpu->arch.vmsa_encrypted)
>> +		return 1;
> 
> A better approach is to refactor need_emulation_on_page_fault() (the hook
> that's just out of sight in this patch) into a more generic
> kvm_x86_ops.is_emulatable() so that the latter can be used to kill emulation
> everywhere, and for other reasons.  E.g. TDX obviously shares very similar
> logic, but SGX also adds a case where KVM can theoretically end up in an
> emulator path without the ability to access the necessary guest state.
> 
> I have exactly such a prep patch (because SGX and TDX...), I'll get it posted
> in the next day or two.

Sounds good. I'll check it out when it's posted.

Thanks,
Tom

> 
>> +
>>  	/*
>>  	 * On AMD platforms, under certain conditions insn_len may be zero on #NPF.
>>  	 * This can happen if a guest gets a page-fault on data access but the HW
>> -- 
>> 2.28.0
>>
diff mbox series

Patch

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index a5d0207e7189..2e1b8b876286 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -5485,6 +5485,13 @@  int kvm_mmu_page_fault(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa, u64 error_code,
 	if (!mmio_info_in_cache(vcpu, cr2_or_gpa, direct) && !is_guest_mode(vcpu))
 		emulation_type |= EMULTYPE_ALLOW_RETRY_PF;
 emulate:
+	/*
+	 * When the guest is an SEV-ES guest, emulation is not possible.  Allow
+	 * the guest to handle the MMIO emulation.
+	 */
+	if (vcpu->arch.vmsa_encrypted)
+		return 1;
+
 	/*
 	 * On AMD platforms, under certain conditions insn_len may be zero on #NPF.
 	 * This can happen if a guest gets a page-fault on data access but the HW