Open code an equivalent of kvm_vcpu_gfn_to_memslot() when querying the
host page size to avoid the "writable" check in __gfn_to_hva_many(),
which will always fail on read-only memslots due to gfn_to_hva()
assuming writes. Functionally, this allows x86 to create large mappings
for read-only memslots that are backed by HugeTLB mappings.
Note, the changelog for commit 05da45583de9 ("KVM: MMU: large page
support") states "If the largepage contains write-protected pages, a
large pte is not used.", but "write-protected" refers to pages that are
temporarily read-only, e.g. read-only memslots didn't even exist at the
time.
Fixes: 4d8b81abc47b ("KVM: introduce readonly memslot")
Cc: [email protected]
Signed-off-by: Sean Christopherson <[email protected]>
---
virt/kvm/kvm_main.c | 12 ++++++++++--
1 file changed, 10 insertions(+), 2 deletions(-)
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 5f7f06824c2b..d9aced677ddd 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -1418,15 +1418,23 @@ EXPORT_SYMBOL_GPL(kvm_is_visible_gfn);
unsigned long kvm_host_page_size(struct kvm_vcpu *vcpu, gfn_t gfn)
{
+ struct kvm_memory_slot *slot;
struct vm_area_struct *vma;
unsigned long addr, size;
size = PAGE_SIZE;
- addr = kvm_vcpu_gfn_to_hva(vcpu, gfn);
- if (kvm_is_error_hva(addr))
+ /*
+ * Manually do the equivalent of kvm_vcpu_gfn_to_hva() to avoid the
+ * "writable" check in __gfn_to_hva_many(), which will always fail on
+ * read-only memslots due to gfn_to_hva() assuming writes.
+ */
+ slot = kvm_vcpu_gfn_to_memslot(vcpu, gfn);
+ if (!slot || slot->flags & KVM_MEMSLOT_INVALID)
return PAGE_SIZE;
+ addr = __gfn_to_hva_memslot(slot, gfn);
+
down_read(¤t->mm->mmap_sem);
vma = find_vma(current->mm, addr);
if (!vma)
--
2.24.1
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