Re: [RFC 14/33] KVM: x86: Add VTL to the MMU role

[Nicolas Saenz Julienne]

On Wed Nov 8, 2023 at 5:26 PM UTC, Sean Christopherson wrote:
> On Wed, Nov 08, 2023, Nicolas Saenz Julienne wrote:
> > With the upcoming introduction of per-VTL memory protections, make MMU
> > roles VTL aware. This will avoid sharing PTEs between vCPUs that belong
> > to different VTLs, and that have distinct memory access restrictions.
> >
> > Four bits are allocated to store the VTL number in the MMU role, since
> > the TLFS states there is a maximum of 16 levels.
>
> How many does KVM actually allow/support?  Multiplying the number of possible
> roots by 16x is a *major* change.

AFAIK in practice only VTL0/1 are used. Don't know if Microsoft will
come up with more in the future. We could introduce a CAP that expses
the number of supported VTLs to user-space, and leave it as a compile
option.

Re: [RFC 14/33] KVM: x86: Add VTL to the MMU role

[Sean Christopherson]

On Wed, Nov 08, 2023, Nicolas Saenz Julienne wrote:
> With the upcoming introduction of per-VTL memory protections, make MMU
> roles VTL aware. This will avoid sharing PTEs between vCPUs that belong
> to different VTLs, and that have distinct memory access restrictions.
> 
> Four bits are allocated to store the VTL number in the MMU role, since
> the TLFS states there is a maximum of 16 levels.

How many does KVM actually allow/support?  Multiplying the number of possible
roots by 16x is a *major* change.

[RFC 14/33] KVM: x86: Add VTL to the MMU role

[Nicolas Saenz Julienne]

With the upcoming introduction of per-VTL memory protections, make MMU
roles VTL aware. This will avoid sharing PTEs between vCPUs that belong
to different VTLs, and that have distinct memory access restrictions.

Four bits are allocated to store the VTL number in the MMU role, since
the TLFS states there is a maximum of 16 levels.

Signed-off-by: Nicolas Saenz Julienne 
---
 arch/x86/include/asm/kvm_host.h | 3 ++-
 arch/x86/kvm/hyperv.h   | 6 ++
 arch/x86/kvm/mmu.h  | 1 +
 arch/x86/kvm/mmu/mmu.c  | 3 +++
 4 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 7712e31b7537..1f5a85d461ce 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -338,7 +338,8 @@ union kvm_mmu_page_role {
unsigned ad_disabled:1;
unsigned guest_mode:1;
unsigned passthrough:1;
-   unsigned :5;
+   unsigned vtl:4;
+   unsigned :1;
 
/*
 * This is left at the top of the word so that
diff --git a/arch/x86/kvm/hyperv.h b/arch/x86/kvm/hyperv.h
index b3d1113efe82..605e80b9e5eb 100644
--- a/arch/x86/kvm/hyperv.h
+++ b/arch/x86/kvm/hyperv.h
@@ -263,4 +263,10 @@ static inline bool kvm_hv_vsm_enabled(struct kvm *kvm)
 
 int kvm_vm_ioctl_get_hv_vsm_state(struct kvm *kvm, struct kvm_hv_vsm_state 
*state);
 
+static inline void kvm_mmu_role_set_hv_bits(struct kvm_vcpu *vcpu,
+   union kvm_mmu_page_role *role)
+{
+   role->vtl = kvm_hv_get_active_vtl(vcpu);
+}
+
 #endif
diff --git a/arch/x86/kvm/mmu.h b/arch/x86/kvm/mmu.h
index 253fb2093d5d..e170388c6da1 100644
--- a/arch/x86/kvm/mmu.h
+++ b/arch/x86/kvm/mmu.h
@@ -304,4 +304,5 @@ static inline gpa_t kvm_translate_gpa(struct kvm_vcpu *vcpu,
return gpa;
return translate_nested_gpa(vcpu, gpa, access, exception);
 }
+
 #endif
diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index baeba8fc1c38..2afef86863fb 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -28,6 +28,7 @@
 #include "page_track.h"
 #include "cpuid.h"
 #include "spte.h"
+#include "hyperv.h"
 
 #include 
 #include 
@@ -5197,6 +5198,7 @@ static union kvm_cpu_role kvm_calc_cpu_role(struct 
kvm_vcpu *vcpu,
role.base.smm = is_smm(vcpu);
role.base.guest_mode = is_guest_mode(vcpu);
role.ext.valid = 1;
+   kvm_mmu_role_set_hv_bits(vcpu, &role.base);
 
if (!is_cr0_pg(regs)) {
role.base.direct = 1;
@@ -5271,6 +5273,7 @@ kvm_calc_tdp_mmu_root_page_role(struct kvm_vcpu *vcpu,
role.level = kvm_mmu_get_tdp_level(vcpu);
role.direct = true;
role.has_4_byte_gpte = false;
+   kvm_mmu_role_set_hv_bits(vcpu, &role);
 
return role;
 }
-- 
2.40.1