2020-03-03 00:00:26

by Sean Christopherson

Subject: [PATCH v2 64/66] KVM: nSVM: Expose SVM features to L1 iff nested is enabled

Set SVM feature bits in KVM capabilities if and only if nested=true, KVM
shouldn't advertise features that realistically can't be used. Use
kvm_cpu_cap_has(X86_FEATURE_SVM) to indirectly query "nested" in
svm_set_supported_cpuid() in anticipation of moving CPUID 0x8000000A
adjustments into common x86 code.

Suggested-by: Paolo Bonzini <[email protected]>
Signed-off-by: Sean Christopherson <[email protected]>
---
arch/x86/kvm/svm.c | 22 +++++++++++++---------
1 file changed, 13 insertions(+), 9 deletions(-)

diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index f32fc3c03667..8e39dcd3160d 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -1373,21 +1373,21 @@ static __init void svm_set_cpu_caps(void)
if (avic)
kvm_cpu_cap_clear(X86_FEATURE_X2APIC);

- /* CPUID 0x80000001 */
- if (nested)
+ /* CPUID 0x80000001 and 0x8000000A (SVM features) */
+ if (nested) {
kvm_cpu_cap_set(X86_FEATURE_SVM);

+ if (boot_cpu_has(X86_FEATURE_NRIPS))
+ kvm_cpu_cap_set(X86_FEATURE_NRIPS);
+
+ if (npt_enabled)
+ kvm_cpu_cap_set(X86_FEATURE_NPT);
+ }
+
/* CPUID 0x80000008 */
if (boot_cpu_has(X86_FEATURE_LS_CFG_SSBD) ||
boot_cpu_has(X86_FEATURE_AMD_SSBD))
kvm_cpu_cap_set(X86_FEATURE_VIRT_SSBD);
-
- /* CPUID 0x8000000A */
- /* Support next_rip if host supports it */
- kvm_cpu_cap_check_and_set(X86_FEATURE_NRIPS);
-
- if (npt_enabled)
- kvm_cpu_cap_set(X86_FEATURE_NPT);
}

static __init int svm_hardware_setup(void)
@@ -6051,6 +6051,10 @@ static void svm_set_supported_cpuid(struct kvm_cpuid_entry2 *entry)
{
switch (entry->function) {
case 0x8000000A:
+ if (!kvm_cpu_cap_has(X86_FEATURE_SVM)) {
+ entry->eax = entry->ebx = entry->ecx = entry->edx = 0;
+ break;
+ }
entry->eax = 1; /* SVM revision 1 */
entry->ebx = 8; /* Lets support 8 ASIDs in case we add proper
ASID emulation to nested SVM */
--
2.24.1

2020-03-03 16:14:03

by Vitaly Kuznetsov

Subject: Re: [PATCH v2 64/66] KVM: nSVM: Expose SVM features to L1 iff nested is enabled

Sean Christopherson <[email protected]> writes:

> Set SVM feature bits in KVM capabilities if and only if nested=true, KVM
> shouldn't advertise features that realistically can't be used. Use
> kvm_cpu_cap_has(X86_FEATURE_SVM) to indirectly query "nested" in
> svm_set_supported_cpuid() in anticipation of moving CPUID 0x8000000A
> adjustments into common x86 code.
>
> Suggested-by: Paolo Bonzini <[email protected]>
> Signed-off-by: Sean Christopherson <[email protected]>
> ---
> arch/x86/kvm/svm.c | 22 +++++++++++++---------
> 1 file changed, 13 insertions(+), 9 deletions(-)
>
> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
> index f32fc3c03667..8e39dcd3160d 100644
> --- a/arch/x86/kvm/svm.c
> +++ b/arch/x86/kvm/svm.c
> @@ -1373,21 +1373,21 @@ static __init void svm_set_cpu_caps(void)
> if (avic)
> kvm_cpu_cap_clear(X86_FEATURE_X2APIC);
>
> - /* CPUID 0x80000001 */
> - if (nested)
> + /* CPUID 0x80000001 and 0x8000000A (SVM features) */
> + if (nested) {
> kvm_cpu_cap_set(X86_FEATURE_SVM);
>
> + if (boot_cpu_has(X86_FEATURE_NRIPS))
> + kvm_cpu_cap_set(X86_FEATURE_NRIPS);
> +
> + if (npt_enabled)
> + kvm_cpu_cap_set(X86_FEATURE_NPT);
> + }
> +
> /* CPUID 0x80000008 */
> if (boot_cpu_has(X86_FEATURE_LS_CFG_SSBD) ||
> boot_cpu_has(X86_FEATURE_AMD_SSBD))
> kvm_cpu_cap_set(X86_FEATURE_VIRT_SSBD);
> -
> - /* CPUID 0x8000000A */
> - /* Support next_rip if host supports it */
> - kvm_cpu_cap_check_and_set(X86_FEATURE_NRIPS);
> -
> - if (npt_enabled)
> - kvm_cpu_cap_set(X86_FEATURE_NPT);
> }
>
> static __init int svm_hardware_setup(void)
> @@ -6051,6 +6051,10 @@ static void svm_set_supported_cpuid(struct kvm_cpuid_entry2 *entry)
> {
> switch (entry->function) {
> case 0x8000000A:
> + if (!kvm_cpu_cap_has(X86_FEATURE_SVM)) {
> + entry->eax = entry->ebx = entry->ecx = entry->edx = 0;
> + break;
> + }
> entry->eax = 1; /* SVM revision 1 */
> entry->ebx = 8; /* Lets support 8 ASIDs in case we add proper
> ASID emulation to nested SVM */

Reviewed-by: Vitaly Kuznetsov <[email protected]>

--
Vitaly

2020-03-03 21:39:09

by Jim Mattson

Subject: Re: [PATCH v2 64/66] KVM: nSVM: Expose SVM features to L1 iff nested is enabled

On Mon, Mar 2, 2020 at 3:57 PM Sean Christopherson
<[email protected]> wrote:
>
> Set SVM feature bits in KVM capabilities if and only if nested=true, KVM
> shouldn't advertise features that realistically can't be used. Use
> kvm_cpu_cap_has(X86_FEATURE_SVM) to indirectly query "nested" in
> svm_set_supported_cpuid() in anticipation of moving CPUID 0x8000000A
> adjustments into common x86 code.

Why not go ahead and report the SVM feature bits regardless of
"nested," and lock SVM off in VM_CR when nested=false? That would be
more like hardware behavior.