[patch 2/3] KVM: dont require read-only host ptes

Marcelo Tosatti
2010-10-05T12:17:37Z

[-- Attachment #1: gfn-to-pfn-ronly --]
[-- Type: text/plain, Size: 7088 bytes --]

gfn_to_pfn requires a writable host pte, failing otherwise.

Change it to fallback to read-only "acquision', informing the callers.

Hopefully the ptes are cache-hot so the overhead is minimal.

Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

Index: kvm/arch/ia64/kvm/kvm-ia64.c
===================================================================
--- kvm.orig/arch/ia64/kvm/kvm-ia64.c
+++ kvm/arch/ia64/kvm/kvm-ia64.c
@@ -1589,7 +1589,7 @@ int kvm_arch_prepare_memory_region(struc
return -ENOMEM;

for (i = 0; i < npages; i++) {
- pfn = gfn_to_pfn(kvm, base_gfn + i);
+ pfn = gfn_to_pfn(kvm, base_gfn + i, NULL);
if (!kvm_is_mmio_pfn(pfn)) {
kvm_set_pmt_entry(kvm, base_gfn + i,
pfn << PAGE_SHIFT,
Index: kvm/arch/x86/kvm/mmu.c
===================================================================
--- kvm.orig/arch/x86/kvm/mmu.c
+++ kvm/arch/x86/kvm/mmu.c
@@ -2273,6 +2273,7 @@ static int nonpaging_map(struct kvm_vcpu
{
int r;
int level;
+ int writable;
pfn_t pfn;
unsigned long mmu_seq;

@@ -2289,10 +2290,10 @@ static int nonpaging_map(struct kvm_vcpu

mmu_seq = vcpu->kvm->mmu_notifier_seq;
smp_rmb();
- pfn = gfn_to_pfn(vcpu->kvm, gfn);
+ pfn = gfn_to_pfn(vcpu->kvm, gfn, &writable);

/* mmio */
- if (is_error_pfn(pfn))
+ if (is_error_pfn(pfn) || !writable)
return kvm_handle_bad_page(vcpu->kvm, gfn, pfn);

spin_lock(&vcpu->kvm->mmu_lock);
@@ -2581,6 +2582,8 @@ static int tdp_page_fault(struct kvm_vcp
pfn_t pfn;
int r;
int level;
+ int writable;
+ int write = error_code & PFERR_WRITE_MASK;
gfn_t gfn = gpa >> PAGE_SHIFT;
unsigned long mmu_seq;

@@ -2597,15 +2600,14 @@ static int tdp_page_fault(struct kvm_vcp

mmu_seq = vcpu->kvm->mmu_notifier_seq;
smp_rmb();
- pfn = gfn_to_pfn(vcpu->kvm, gfn);
- if (is_error_pfn(pfn))
+ pfn = gfn_to_pfn(vcpu->kvm, gfn, &writable);
+ if (is_error_pfn(pfn) || !writable)
return kvm_handle_bad_page(vcpu->kvm, gfn, pfn);
spin_lock(&vcpu->kvm->mmu_lock);
if (mmu_notifier_retry(vcpu, mmu_seq))
goto out_unlock;
kvm_mmu_free_some_pages(vcpu);
- r = __direct_map(vcpu, gpa, error_code & PFERR_WRITE_MASK,
- level, gfn, pfn);
+ r = __direct_map(vcpu, gpa, write, level, gfn, pfn);
spin_unlock(&vcpu->kvm->mmu_lock);

return r;
@@ -3043,6 +3045,7 @@ static void mmu_guess_page_from_pte_writ
{
gfn_t gfn;
pfn_t pfn;
+ int writable;

if (!is_present_gpte(gpte))
return;
@@ -3050,9 +3053,9 @@ static void mmu_guess_page_from_pte_writ

vcpu->arch.update_pte.mmu_seq = vcpu->kvm->mmu_notifier_seq;
smp_rmb();
- pfn = gfn_to_pfn(vcpu->kvm, gfn);
+ pfn = gfn_to_pfn(vcpu->kvm, gfn, &writable);

- if (is_error_pfn(pfn)) {
+ if (is_error_pfn(pfn) || !writable) {
kvm_release_pfn_clean(pfn);
return;
}
Index: kvm/arch/x86/kvm/paging_tmpl.h
===================================================================
--- kvm.orig/arch/x86/kvm/paging_tmpl.h
+++ kvm/arch/x86/kvm/paging_tmpl.h
@@ -536,6 +536,7 @@ static int FNAME(page_fault)(struct kvm_
int write_fault = error_code & PFERR_WRITE_MASK;
int user_fault = error_code & PFERR_USER_MASK;
int fetch_fault = error_code & PFERR_FETCH_MASK;
+ int writable;
struct guest_walker walker;
u64 *sptep;
int write_pt = 0;
@@ -573,10 +574,10 @@ static int FNAME(page_fault)(struct kvm_

mmu_seq = vcpu->kvm->mmu_notifier_seq;
smp_rmb();
- pfn = gfn_to_pfn(vcpu->kvm, walker.gfn);
+ pfn = gfn_to_pfn(vcpu->kvm, walker.gfn, &writable);

/* mmio */
- if (is_error_pfn(pfn))
+ if (is_error_pfn(pfn) || !writable)
return kvm_handle_bad_page(vcpu->kvm, walker.gfn, pfn);

spin_lock(&vcpu->kvm->mmu_lock);
Index: kvm/include/linux/kvm_host.h
===================================================================
--- kvm.orig/include/linux/kvm_host.h
+++ kvm/include/linux/kvm_host.h
@@ -302,7 +302,7 @@ void kvm_set_page_accessed(struct page *

pfn_t hva_to_pfn_atomic(struct kvm *kvm, unsigned long addr);
pfn_t gfn_to_pfn_atomic(struct kvm *kvm, gfn_t gfn);
-pfn_t gfn_to_pfn(struct kvm *kvm, gfn_t gfn);
+pfn_t gfn_to_pfn(struct kvm *kvm, gfn_t gfn, int *writable);
pfn_t gfn_to_pfn_memslot(struct kvm *kvm,
struct kvm_memory_slot *slot, gfn_t gfn);
int memslot_id(struct kvm *kvm, gfn_t gfn);
Index: kvm/virt/kvm/kvm_main.c
===================================================================
--- kvm.orig/virt/kvm/kvm_main.c
+++ kvm/virt/kvm/kvm_main.c
@@ -948,17 +948,28 @@ unsigned long gfn_to_hva(struct kvm *kvm
}
EXPORT_SYMBOL_GPL(gfn_to_hva);

-static pfn_t hva_to_pfn(struct kvm *kvm, unsigned long addr, bool atomic)
+static pfn_t hva_to_pfn(struct kvm *kvm, unsigned long addr, bool atomic,
+ int *writable)
{
struct page *page[1];
int npages;
pfn_t pfn;

+ if (writable)
+ *writable = 1;
+
if (atomic)
npages = __get_user_pages_fast(addr, 1, 1, page);
else {
might_sleep();
npages = get_user_pages_fast(addr, 1, 1, page);
+
+ /* attempt to map read-only */
+ if (unlikely(npages != 1) && writable) {
+ npages = get_user_pages_fast(addr, 1, 0, page);
+ if (npages == 1)
+ *writable = 0;
+ }
}

if (unlikely(npages != 1)) {
@@ -995,11 +1006,11 @@ return_fault_page:

pfn_t hva_to_pfn_atomic(struct kvm *kvm, unsigned long addr)
{
- return hva_to_pfn(kvm, addr, true);
+ return hva_to_pfn(kvm, addr, true, NULL);
}
EXPORT_SYMBOL_GPL(hva_to_pfn_atomic);

-static pfn_t __gfn_to_pfn(struct kvm *kvm, gfn_t gfn, bool atomic)
+static pfn_t __gfn_to_pfn(struct kvm *kvm, gfn_t gfn, bool atomic, int *writable)
{
unsigned long addr;

@@ -1009,18 +1020,18 @@ static pfn_t __gfn_to_pfn(struct kvm *kv
return page_to_pfn(bad_page);
}

- return hva_to_pfn(kvm, addr, atomic);
+ return hva_to_pfn(kvm, addr, atomic, writable);
}

pfn_t gfn_to_pfn_atomic(struct kvm *kvm, gfn_t gfn)
{
- return __gfn_to_pfn(kvm, gfn, true);
+ return __gfn_to_pfn(kvm, gfn, true, NULL);
}
EXPORT_SYMBOL_GPL(gfn_to_pfn_atomic);

-pfn_t gfn_to_pfn(struct kvm *kvm, gfn_t gfn)
+pfn_t gfn_to_pfn(struct kvm *kvm, gfn_t gfn, int *writable)
{
- return __gfn_to_pfn(kvm, gfn, false);
+ return __gfn_to_pfn(kvm, gfn, false, writable);
}
EXPORT_SYMBOL_GPL(gfn_to_pfn);

@@ -1028,7 +1039,7 @@ pfn_t gfn_to_pfn_memslot(struct kvm *kvm
struct kvm_memory_slot *slot, gfn_t gfn)
{
unsigned long addr = gfn_to_hva_memslot(slot, gfn);
- return hva_to_pfn(kvm, addr, false);
+ return hva_to_pfn(kvm, addr, false, NULL);
}

int gfn_to_page_many_atomic(struct kvm *kvm, gfn_t gfn, struct page **pages,
@@ -1052,7 +1063,7 @@ struct page *gfn_to_page(struct kvm *kvm
{
pfn_t pfn;

- pfn = gfn_to_pfn(kvm, gfn);
+ pfn = gfn_to_pfn(kvm, gfn, NULL);
if (!kvm_is_mmio_pfn(pfn))
return pfn_to_page(pfn);

Index: kvm/arch/powerpc/kvm/book3s.c
===================================================================
--- kvm.orig/arch/powerpc/kvm/book3s.c
+++ kvm/arch/powerpc/kvm/book3s.c
@@ -468,7 +468,7 @@ pfn_t kvmppc_gfn_to_pfn(struct kvm_vcpu
return pfn;
}

- return gfn_to_pfn(vcpu->kvm, gfn);
+ return gfn_to_pfn(vcpu->kvm, gfn, NULL);
}

/* Book3s_32 CPUs always have 32 bytes cache line size, which Linux assumes. To