[PATCH v1 5/6] KVM: arm64: Use kvm_s2_fault_vma_info in gmem_abort()

[Vincent Donnefort]

From: Fuad Tabba <fuad.tabba at linux.dev>

gmem_abort() maps at s2fd->fault_ipa, which HPFAR_EL2 holds at 4K
granularity whatever the page size. The generic page-table code aligns
it, but pkvm_pgtable_stage2_map() looks up existing mappings over
[addr, addr + size), so on a pKVM host with pages larger than 4K a
guest_memfd-backed guest that faults past the first 4K of a page can
find its neighbour's mapping, get -EAGAIN and take the same fault
forever.

Take the addresses from kvm_s2_fault_vma_info instead, as
user_mem_abort() does, and report the gfn kvm_gmem_get_pfn() failed on
in the memory fault exit. kvm_s2_fault_get_vma_info() itself isn't
called: a guest_memfd memslot's userspace_addr doesn't need to be
backed by a VMA.

Fixes: a7b57e0995927 ("KVM: arm64: Handle guest_memfd-backed guest page faults")
Reported-by: Sashiko <sashiko-bot at kernel.org>
Closes: https://lore.kernel.org/r/20260913175105.A57AC1F000FF@smtp.kernel.org
Cc: stable at vger.kernel.org
Signed-off-by: Fuad Tabba <fuad.tabba at linux.dev>
Signed-off-by: Vincent Donnefort <vdonnefort at google.com>
---
 arch/arm64/kvm/mmu.c | 28 +++++++++++++---------------
 1 file changed, 13 insertions(+), 15 deletions(-)

diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
index 5aac624b0442..ee0fcca838c1 100644
--- a/arch/arm64/kvm/mmu.c
+++ b/arch/arm64/kvm/mmu.c
@@ -1953,11 +1953,9 @@ static int gmem_abort(const struct kvm_s2_fault_desc *s2fd)
 	enum kvm_pgtable_walk_flags flags = KVM_PGTABLE_WALK_SHARED;
 	enum kvm_pgtable_prot prot = KVM_PGTABLE_PROT_R;
 	struct kvm_pgtable *pgt = s2fd->vcpu->arch.hw_mmu->pgt;
-	unsigned long mmu_seq;
-	struct page *page;
+	struct kvm_s2_fault_vma_info s2vi = {};
 	struct kvm *kvm = s2fd->vcpu->kvm;
 	void *memcache = NULL;
-	kvm_pfn_t pfn;
 	gfn_t gfn;
 	int ret;
 
@@ -1968,23 +1966,22 @@ static int gmem_abort(const struct kvm_s2_fault_desc *s2fd)
 			return ret;
 	}
 
-	if (s2fd->nested)
-		gfn = kvm_s2_trans_output(s2fd->nested) >> PAGE_SHIFT;
-	else
-		gfn = s2fd->fault_ipa >> PAGE_SHIFT;
+	s2vi.vma_pagesize = PAGE_SIZE;
+	s2vi.gfn = ALIGN_DOWN(s2fd->fault_ipa, s2vi.vma_pagesize) >> PAGE_SHIFT;
+	gfn = get_canonical_gfn(s2fd, &s2vi);
 
 	write_fault = kvm_is_write_fault(s2fd->vcpu);
 	exec_fault = kvm_vcpu_trap_is_exec_fault(s2fd->vcpu);
 
 	VM_WARN_ON_ONCE(write_fault && exec_fault);
 
-	mmu_seq = kvm->mmu_invalidate_seq;
+	s2vi.mmu_seq = kvm->mmu_invalidate_seq;
 	/* Pairs with the smp_wmb() in kvm_mmu_invalidate_end(). */
 	smp_rmb();
 
-	ret = kvm_gmem_get_pfn(kvm, s2fd->memslot, gfn, &pfn, &page, NULL);
+	ret = kvm_gmem_get_pfn(kvm, s2fd->memslot, gfn, &s2vi.pfn, &s2vi.page, NULL);
 	if (ret) {
-		kvm_prepare_memory_fault_exit(s2fd->vcpu, s2fd->fault_ipa, PAGE_SIZE,
+		kvm_prepare_memory_fault_exit(s2fd->vcpu, gfn_to_gpa(gfn), s2vi.vma_pagesize,
 					      write_fault, exec_fault, false);
 		return ret;
 	}
@@ -2002,7 +1999,7 @@ static int gmem_abort(const struct kvm_s2_fault_desc *s2fd)
 		prot = adjust_nested_exec_perms(kvm, s2fd->nested, prot);
 
 	kvm_fault_lock(kvm);
-	if (mmu_invalidate_retry(kvm, mmu_seq)) {
+	if (mmu_invalidate_retry(kvm, s2vi.mmu_seq)) {
 		ret = -EAGAIN;
 		goto out_unlock;
 	}
@@ -2013,16 +2010,17 @@ static int gmem_abort(const struct kvm_s2_fault_desc *s2fd)
 		 * PTE, which will be preserved.
 		 */
 		prot &= ~KVM_NV_GUEST_MAP_SZ;
-		ret = KVM_PGT_FN(kvm_pgtable_stage2_relax_perms)(pgt, s2fd->fault_ipa,
+		ret = KVM_PGT_FN(kvm_pgtable_stage2_relax_perms)(pgt, gfn_to_gpa(s2vi.gfn),
 								 prot, flags);
 	} else {
-		ret = KVM_PGT_FN(kvm_pgtable_stage2_map)(pgt, s2fd->fault_ipa, PAGE_SIZE,
-							 __pfn_to_phys(pfn), prot,
+		ret = KVM_PGT_FN(kvm_pgtable_stage2_map)(pgt, gfn_to_gpa(s2vi.gfn),
+							 s2vi.vma_pagesize,
+							 __pfn_to_phys(s2vi.pfn), prot,
 							 memcache, flags);
 	}
 
 out_unlock:
-	kvm_release_faultin_page(kvm, page, !!ret, prot & KVM_PGTABLE_PROT_W);
+	kvm_release_faultin_page(kvm, s2vi.page, !!ret, prot & KVM_PGTABLE_PROT_W);
 	kvm_fault_unlock(kvm);
 
 	if ((prot & KVM_PGTABLE_PROT_W) && !ret)
-- 
2.55.0.1082.g2b9226bbc0-goog