[PATCH v2 01/25] KVM: x86/mmu: avoid indirect call for get_cr3

Paolo Bonzini
2022-02-21T16:23:07Z

Most of the time, calls to get_guest_pgd result in calling kvm_read_cr3
(the exception is only nested TDP). Check if that is the case if
retpolines are enabled, thus avoiding an expensive indirect call.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
arch/x86/kvm/mmu.h | 10 ++++++++++
arch/x86/kvm/mmu/mmu.c | 15 ++++++++-------
arch/x86/kvm/mmu/paging_tmpl.h | 2 +-
arch/x86/kvm/x86.c | 2 +-
4 files changed, 20 insertions(+), 9 deletions(-)

diff --git a/arch/x86/kvm/mmu.h b/arch/x86/kvm/mmu.h
index 1d0c1904d69a..6ee4436e46f1 100644
--- a/arch/x86/kvm/mmu.h
+++ b/arch/x86/kvm/mmu.h
@@ -116,6 +116,16 @@ static inline void kvm_mmu_load_pgd(struct kvm_vcpu *vcpu)
vcpu->arch.mmu->shadow_root_level);
}

+extern unsigned long kvm_get_guest_cr3(struct kvm_vcpu *vcpu);
+static inline unsigned long kvm_mmu_get_guest_pgd(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu)
+{
+#ifdef CONFIG_RETPOLINE
+ if (mmu->get_guest_pgd == kvm_get_guest_cr3)
+ return kvm_read_cr3(vcpu);
+#endif
+ return mmu->get_guest_pgd(vcpu);
+}
+
struct kvm_page_fault {
/* arguments to kvm_mmu_do_page_fault. */
const gpa_t addr;
diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index b2c1c4eb6007..7051040e15b3 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -3435,7 +3435,7 @@ static int mmu_alloc_shadow_roots(struct kvm_vcpu *vcpu)
unsigned i;
int r;

- root_pgd = mmu->get_guest_pgd(vcpu);
+ root_pgd = kvm_mmu_get_guest_pgd(vcpu, mmu);
root_gfn = root_pgd >> PAGE_SHIFT;

if (mmu_check_root(vcpu, root_gfn))
@@ -3854,12 +3854,13 @@ static void shadow_page_table_clear_flood(struct kvm_vcpu *vcpu, gva_t addr)
static bool kvm_arch_setup_async_pf(struct kvm_vcpu *vcpu, gpa_t cr2_or_gpa,
gfn_t gfn)
{
+ struct kvm_mmu *mmu = vcpu->arch.mmu;
struct kvm_arch_async_pf arch;

arch.token = (vcpu->arch.apf.id++ << 12) | vcpu->vcpu_id;
arch.gfn = gfn;
- arch.direct_map = vcpu->arch.mmu->direct_map;
- arch.cr3 = vcpu->arch.mmu->get_guest_pgd(vcpu);
+ arch.direct_map = mmu->direct_map;
+ arch.cr3 = kvm_mmu_get_guest_pgd(vcpu, mmu);

return kvm_setup_async_pf(vcpu, cr2_or_gpa,
kvm_vcpu_gfn_to_hva(vcpu, gfn), &arch);
@@ -4208,7 +4209,7 @@ void kvm_mmu_new_pgd(struct kvm_vcpu *vcpu, gpa_t new_pgd)
}
EXPORT_SYMBOL_GPL(kvm_mmu_new_pgd);

-static unsigned long get_cr3(struct kvm_vcpu *vcpu)
+unsigned long kvm_get_guest_cr3(struct kvm_vcpu *vcpu)
{
return kvm_read_cr3(vcpu);
}
@@ -4767,7 +4768,7 @@ static void init_kvm_tdp_mmu(struct kvm_vcpu *vcpu)
context->invlpg = NULL;
context->shadow_root_level = kvm_mmu_get_tdp_level(vcpu);
context->direct_map = true;
- context->get_guest_pgd = get_cr3;
+ context->get_guest_pgd = kvm_get_guest_cr3;
context->get_pdptr = kvm_pdptr_read;
context->inject_page_fault = kvm_inject_page_fault;
context->root_level = role_regs_to_root_level(&regs);
@@ -4942,7 +4943,7 @@ static void init_kvm_softmmu(struct kvm_vcpu *vcpu)

kvm_init_shadow_mmu(vcpu, &regs);

- context->get_guest_pgd = get_cr3;
+ context->get_guest_pgd = kvm_get_guest_cr3;
context->get_pdptr = kvm_pdptr_read;
context->inject_page_fault = kvm_inject_page_fault;
}
@@ -4974,7 +4975,7 @@ static void init_kvm_nested_mmu(struct kvm_vcpu *vcpu)
return;

g_context->mmu_role.as_u64 = new_role.as_u64;
- g_context->get_guest_pgd = get_cr3;
+ g_context->get_guest_pgd = kvm_get_guest_cr3;
g_context->get_pdptr = kvm_pdptr_read;
g_context->inject_page_fault = kvm_inject_page_fault;
g_context->root_level = new_role.base.level;
diff --git a/arch/x86/kvm/mmu/paging_tmpl.h b/arch/x86/kvm/mmu/paging_tmpl.h
index 252c77805eb9..80b4b291002a 100644
--- a/arch/x86/kvm/mmu/paging_tmpl.h
+++ b/arch/x86/kvm/mmu/paging_tmpl.h
@@ -362,7 +362,7 @@ static int FNAME(walk_addr_generic)(struct guest_walker *walker,
trace_kvm_mmu_pagetable_walk(addr, access);
retry_walk:
walker->level = mmu->root_level;
- pte = mmu->get_guest_pgd(vcpu);
+ pte = kvm_mmu_get_guest_pgd(vcpu, mmu);
have_ad = PT_HAVE_ACCESSED_DIRTY(mmu);

#if PTTYPE == 64
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 6552360d8888..da33d3a88a8d 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -12190,7 +12190,7 @@ void kvm_arch_async_page_ready(struct kvm_vcpu *vcpu, struct kvm_async_pf *work)
return;

if (!vcpu->arch.mmu->direct_map &&
- work->arch.cr3 != vcpu->arch.mmu->get_guest_pgd(vcpu))
+ work->arch.cr3 != kvm_mmu_get_guest_pgd(vcpu, vcpu->arch.mmu))
return;

kvm_mmu_do_page_fault(vcpu, work->cr2_or_gpa, 0, true);
--
2.31.1