[PATCH v5 05/21] KVM: x86/mmu: Decompose kvm_mmu_get_page() into separate functions

David Matlack
2022-05-13T20:28:45Z

Decompose kvm_mmu_get_page() into separate helper functions to increase
readability and prepare for allocating shadow pages without a vcpu
pointer.

Specifically, pull the guts of kvm_mmu_get_page() into 2 helper
functions:

kvm_mmu_find_shadow_page() -
Walks the page hash checking for any existing mmu pages that match the
given gfn and role.

kvm_mmu_alloc_shadow_page()
Allocates and initializes an entirely new kvm_mmu_page. This currently
requries a vcpu pointer for allocation and looking up the memslot but
that will be removed in a future commit.

No functional change intended.

Reviewed-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: David Matlack <dmatlack@google.com>
---
arch/x86/kvm/mmu/mmu.c | 52 +++++++++++++++++++++++++++++++-----------
1 file changed, 39 insertions(+), 13 deletions(-)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 34786244ebad..ce334eaeef22 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -2019,16 +2019,16 @@ static void clear_sp_write_flooding_count(u64 *spte)
__clear_sp_write_flooding_count(sptep_to_sp(spte));
}

-static struct kvm_mmu_page *kvm_mmu_get_page(struct kvm_vcpu *vcpu, gfn_t gfn,
- union kvm_mmu_page_role role)
+static struct kvm_mmu_page *kvm_mmu_find_shadow_page(struct kvm_vcpu *vcpu,
+ gfn_t gfn,
+ struct hlist_head *sp_list,
+ union kvm_mmu_page_role role)
{
- struct hlist_head *sp_list;
struct kvm_mmu_page *sp;
int ret;
int collisions = 0;
LIST_HEAD(invalid_list);

- sp_list = &vcpu->kvm->arch.mmu_page_hash[kvm_page_table_hashfn(gfn)];
for_each_valid_sp(vcpu->kvm, sp, sp_list) {
if (sp->gfn != gfn) {
collisions++;
@@ -2053,7 +2053,7 @@ static struct kvm_mmu_page *kvm_mmu_get_page(struct kvm_vcpu *vcpu, gfn_t gfn,

/* unsync and write-flooding only apply to indirect SPs. */
if (sp->role.direct)
- goto trace_get_page;
+ goto out;

if (sp->unsync) {
/*
@@ -2079,14 +2079,26 @@ static struct kvm_mmu_page *kvm_mmu_get_page(struct kvm_vcpu *vcpu, gfn_t gfn,

__clear_sp_write_flooding_count(sp);

-trace_get_page:
- trace_kvm_mmu_get_page(sp, false);
goto out;
}

+ sp = NULL;
++vcpu->kvm->stat.mmu_cache_miss;

- sp = kvm_mmu_alloc_page(vcpu, role.direct);
+out:
+ kvm_mmu_commit_zap_page(vcpu->kvm, &invalid_list);
+
+ if (collisions > vcpu->kvm->stat.max_mmu_page_hash_collisions)
+ vcpu->kvm->stat.max_mmu_page_hash_collisions = collisions;
+ return sp;
+}
+
+static struct kvm_mmu_page *kvm_mmu_alloc_shadow_page(struct kvm_vcpu *vcpu,
+ gfn_t gfn,
+ struct hlist_head *sp_list,
+ union kvm_mmu_page_role role)
+{
+ struct kvm_mmu_page *sp = kvm_mmu_alloc_page(vcpu, role.direct);

sp->gfn = gfn;
sp->role = role;
@@ -2096,12 +2108,26 @@ static struct kvm_mmu_page *kvm_mmu_get_page(struct kvm_vcpu *vcpu, gfn_t gfn,
if (role.level == PG_LEVEL_4K && kvm_vcpu_write_protect_gfn(vcpu, gfn))
kvm_flush_remote_tlbs_with_address(vcpu->kvm, gfn, 1);
}
- trace_kvm_mmu_get_page(sp, true);
-out:
- kvm_mmu_commit_zap_page(vcpu->kvm, &invalid_list);

- if (collisions > vcpu->kvm->stat.max_mmu_page_hash_collisions)
- vcpu->kvm->stat.max_mmu_page_hash_collisions = collisions;
+ return sp;
+}
+
+static struct kvm_mmu_page *kvm_mmu_get_page(struct kvm_vcpu *vcpu, gfn_t gfn,
+ union kvm_mmu_page_role role)
+{
+ struct hlist_head *sp_list;
+ struct kvm_mmu_page *sp;
+ bool created = false;
+
+ sp_list = &vcpu->kvm->arch.mmu_page_hash[kvm_page_table_hashfn(gfn)];
+
+ sp = kvm_mmu_find_shadow_page(vcpu, gfn, sp_list, role);
+ if (!sp) {
+ created = true;
+ sp = kvm_mmu_alloc_shadow_page(vcpu, gfn, sp_list, role);
+ }
+
+ trace_kvm_mmu_get_page(sp, created);
return sp;
}

--
2.36.0.550.gb090851708-goog