[PATCH v13 33/85] KVM: Pass in write/dirty to kvm_vcpu_map(), not kvm_vcpu_unmap()

Sean Christopherson
2024-10-10T21:16:36Z

Now that all kvm_vcpu_{,un}map() users pass "true" for @dirty, have them
pass "true" as a @writable param to kvm_vcpu_map(), and thus create a
read-only mapping when possible.

Note, creating read-only mappings can be theoretically slower, as they
don't play nice with fast GUP due to the need to break CoW before mapping
the underlying PFN. But practically speaking, creating a mapping isn't
a super hot path, and getting a writable mapping for reading is weird and
confusing.

Tested-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
arch/x86/kvm/svm/nested.c | 4 ++--
arch/x86/kvm/svm/sev.c | 2 +-
arch/x86/kvm/svm/svm.c | 8 ++++----
arch/x86/kvm/vmx/nested.c | 16 ++++++++--------
include/linux/kvm_host.h | 20 ++++++++++++++++++--
virt/kvm/kvm_main.c | 12 +++++++-----
6 files changed, 40 insertions(+), 22 deletions(-)

diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
index d5314cb7dff4..9f9478bdecfc 100644
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -922,7 +922,7 @@ int nested_svm_vmrun(struct kvm_vcpu *vcpu)
nested_svm_vmexit(svm);

out:
- kvm_vcpu_unmap(vcpu, &map, true);
+ kvm_vcpu_unmap(vcpu, &map);

return ret;
}
@@ -1126,7 +1126,7 @@ int nested_svm_vmexit(struct vcpu_svm *svm)
vmcb12->control.exit_int_info_err,
KVM_ISA_SVM);

- kvm_vcpu_unmap(vcpu, &map, true);
+ kvm_vcpu_unmap(vcpu, &map);

nested_svm_transition_tlb_flush(vcpu);

diff --git a/arch/x86/kvm/svm/sev.c b/arch/x86/kvm/svm/sev.c
index 0b851ef937f2..4557ff3804ae 100644
--- a/arch/x86/kvm/svm/sev.c
+++ b/arch/x86/kvm/svm/sev.c
@@ -3468,7 +3468,7 @@ void sev_es_unmap_ghcb(struct vcpu_svm *svm)

sev_es_sync_to_ghcb(svm);

- kvm_vcpu_unmap(&svm->vcpu, &svm->sev_es.ghcb_map, true);
+ kvm_vcpu_unmap(&svm->vcpu, &svm->sev_es.ghcb_map);
svm->sev_es.ghcb = NULL;
}

diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 9df3e1e5ae81..c1e29307826b 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -2299,7 +2299,7 @@ static int vmload_vmsave_interception(struct kvm_vcpu *vcpu, bool vmload)
svm_copy_vmloadsave_state(vmcb12, svm->vmcb);
}

- kvm_vcpu_unmap(vcpu, &map, true);
+ kvm_vcpu_unmap(vcpu, &map);

return ret;
}
@@ -4714,7 +4714,7 @@ static int svm_enter_smm(struct kvm_vcpu *vcpu, union kvm_smram *smram)
svm_copy_vmrun_state(map_save.hva + 0x400,
&svm->vmcb01.ptr->save);

- kvm_vcpu_unmap(vcpu, &map_save, true);
+ kvm_vcpu_unmap(vcpu, &map_save);
return 0;
}

@@ -4774,9 +4774,9 @@ static int svm_leave_smm(struct kvm_vcpu *vcpu, const union kvm_smram *smram)
svm->nested.nested_run_pending = 1;

unmap_save:
- kvm_vcpu_unmap(vcpu, &map_save, true);
+ kvm_vcpu_unmap(vcpu, &map_save);
unmap_map:
- kvm_vcpu_unmap(vcpu, &map, true);
+ kvm_vcpu_unmap(vcpu, &map);
return ret;
}

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index ff83b56fe2fa..259fe445e695 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -231,7 +231,7 @@ static inline void nested_release_evmcs(struct kvm_vcpu *vcpu)
struct kvm_vcpu_hv *hv_vcpu = to_hv_vcpu(vcpu);
struct vcpu_vmx *vmx = to_vmx(vcpu);

- kvm_vcpu_unmap(vcpu, &vmx->nested.hv_evmcs_map, true);
+ kvm_vcpu_unmap(vcpu, &vmx->nested.hv_evmcs_map);
vmx->nested.hv_evmcs = NULL;
vmx->nested.hv_evmcs_vmptr = EVMPTR_INVALID;

@@ -318,9 +318,9 @@ static void nested_put_vmcs12_pages(struct kvm_vcpu *vcpu)
{
struct vcpu_vmx *vmx = to_vmx(vcpu);

- kvm_vcpu_unmap(vcpu, &vmx->nested.apic_access_page_map, true);
- kvm_vcpu_unmap(vcpu, &vmx->nested.virtual_apic_map, true);
- kvm_vcpu_unmap(vcpu, &vmx->nested.pi_desc_map, true);
+ kvm_vcpu_unmap(vcpu, &vmx->nested.apic_access_page_map);
+ kvm_vcpu_unmap(vcpu, &vmx->nested.virtual_apic_map);
+ kvm_vcpu_unmap(vcpu, &vmx->nested.pi_desc_map);
vmx->nested.pi_desc = NULL;
}

@@ -624,7 +624,7 @@ static inline bool nested_vmx_prepare_msr_bitmap(struct kvm_vcpu *vcpu,
int msr;
unsigned long *msr_bitmap_l1;
unsigned long *msr_bitmap_l0 = vmx->nested.vmcs02.msr_bitmap;
- struct kvm_host_map msr_bitmap_map;
+ struct kvm_host_map map;

/* Nothing to do if the MSR bitmap is not in use. */
if (!cpu_has_vmx_msr_bitmap() ||
@@ -647,10 +647,10 @@ static inline bool nested_vmx_prepare_msr_bitmap(struct kvm_vcpu *vcpu,
return true;
}

- if (kvm_vcpu_map(vcpu, gpa_to_gfn(vmcs12->msr_bitmap), &msr_bitmap_map))
+ if (kvm_vcpu_map_readonly(vcpu, gpa_to_gfn(vmcs12->msr_bitmap), &map))
return false;

- msr_bitmap_l1 = (unsigned long *)msr_bitmap_map.hva;
+ msr_bitmap_l1 = (unsigned long *)map.hva;

/*
* To keep the control flow simple, pay eight 8-byte writes (sixteen
@@ -714,7 +714,7 @@ static inline bool nested_vmx_prepare_msr_bitmap(struct kvm_vcpu *vcpu,
nested_vmx_set_intercept_for_msr(vmx, msr_bitmap_l1, msr_bitmap_l0,
MSR_IA32_FLUSH_CMD, MSR_TYPE_W);

- kvm_vcpu_unmap(vcpu, &msr_bitmap_map, false);
+ kvm_vcpu_unmap(vcpu, &map);

vmx->nested.force_msr_bitmap_recalc = false;

diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 8739b905d85b..9263375d0362 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -285,6 +285,7 @@ struct kvm_host_map {
void *hva;
kvm_pfn_t pfn;
kvm_pfn_t gfn;
+ bool writable;
};

/*
@@ -1312,8 +1313,23 @@ void mark_page_dirty(struct kvm *kvm, gfn_t gfn);
struct kvm_memslots *kvm_vcpu_memslots(struct kvm_vcpu *vcpu);
struct kvm_memory_slot *kvm_vcpu_gfn_to_memslot(struct kvm_vcpu *vcpu, gfn_t gfn);
kvm_pfn_t kvm_vcpu_gfn_to_pfn(struct kvm_vcpu *vcpu, gfn_t gfn);
-int kvm_vcpu_map(struct kvm_vcpu *vcpu, gpa_t gpa, struct kvm_host_map *map);
-void kvm_vcpu_unmap(struct kvm_vcpu *vcpu, struct kvm_host_map *map, bool dirty);
+
+int __kvm_vcpu_map(struct kvm_vcpu *vcpu, gpa_t gpa, struct kvm_host_map *map,
+ bool writable);
+void kvm_vcpu_unmap(struct kvm_vcpu *vcpu, struct kvm_host_map *map);
+
+static inline int kvm_vcpu_map(struct kvm_vcpu *vcpu, gpa_t gpa,
+ struct kvm_host_map *map)
+{
+ return __kvm_vcpu_map(vcpu, gpa, map, true);
+}
+
+static inline int kvm_vcpu_map_readonly(struct kvm_vcpu *vcpu, gpa_t gpa,
+ struct kvm_host_map *map)
+{
+ return __kvm_vcpu_map(vcpu, gpa, map, false);
+}
+
unsigned long kvm_vcpu_gfn_to_hva(struct kvm_vcpu *vcpu, gfn_t gfn);
unsigned long kvm_vcpu_gfn_to_hva_prot(struct kvm_vcpu *vcpu, gfn_t gfn, bool *writable);
int kvm_vcpu_read_guest_page(struct kvm_vcpu *vcpu, gfn_t gfn, void *data, int offset,
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 40a59526d466..080740f65061 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -3116,7 +3116,8 @@ struct page *gfn_to_page(struct kvm *kvm, gfn_t gfn)
}
EXPORT_SYMBOL_GPL(gfn_to_page);

-int kvm_vcpu_map(struct kvm_vcpu *vcpu, gfn_t gfn, struct kvm_host_map *map)
+int __kvm_vcpu_map(struct kvm_vcpu *vcpu, gfn_t gfn, struct kvm_host_map *map,
+ bool writable)
{
struct kvm_follow_pfn kfp = {
.slot = gfn_to_memslot(vcpu->kvm, gfn),
@@ -3130,6 +3131,7 @@ int kvm_vcpu_map(struct kvm_vcpu *vcpu, gfn_t gfn, struct kvm_host_map *map)
map->page = NULL;
map->hva = NULL;
map->gfn = gfn;
+ map->writable = writable;

map->pfn = kvm_follow_pfn(&kfp);
if (is_error_noslot_pfn(map->pfn))
@@ -3146,9 +3148,9 @@ int kvm_vcpu_map(struct kvm_vcpu *vcpu, gfn_t gfn, struct kvm_host_map *map)

return map->hva ? 0 : -EFAULT;
}
-EXPORT_SYMBOL_GPL(kvm_vcpu_map);
+EXPORT_SYMBOL_GPL(__kvm_vcpu_map);

-void kvm_vcpu_unmap(struct kvm_vcpu *vcpu, struct kvm_host_map *map, bool dirty)
+void kvm_vcpu_unmap(struct kvm_vcpu *vcpu, struct kvm_host_map *map)
{
if (!map->hva)
return;
@@ -3160,11 +3162,11 @@ void kvm_vcpu_unmap(struct kvm_vcpu *vcpu, struct kvm_host_map *map, bool dirty)
memunmap(map->hva);
#endif

- if (dirty)
+ if (map->writable)
kvm_vcpu_mark_page_dirty(vcpu, map->gfn);

if (map->pinned_page) {
- if (dirty)
+ if (map->writable)
kvm_set_page_dirty(map->pinned_page);
kvm_set_page_accessed(map->pinned_page);
unpin_user_page(map->pinned_page);