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[v3,15/22] KVM: x86: Annotate -EFAULTs from direct_map()

Message ID 20230412213510.1220557-16-amoorthy@google.com (mailing list archive)
State New, archived
Headers show
Series Improve scalability of KVM + userfaultfd live migration via annotated memory faults. | expand

Commit Message

Anish Moorthy April 12, 2023, 9:35 p.m. UTC 
Implement KVM_CAP_MEMORY_FAULT_INFO for efaults generated by
direct_map().

Since direct_map() traverses multiple levels of the shadow page table, it
seems like there are actually two correct guest physical address ranges
which could be provided.

1. A smaller range, more specific range, which potentially only
   corresponds to a part of what could not be mapped.
   start = gfn_round_for_level(fault->gfn, fault->goal_level)
   length = KVM_PAGES_PER_HPAGE(fault->goal_level)

2. The entire range which could not be mapped
   start = gfn_round_for_level(fault->gfn, fault->goal_level)
   length = KVM_PAGES_PER_HPAGE(fault->goal_level)

Take the first approach, although it's possible the second is actually
preferable.

Signed-off-by: Anish Moorthy <amoorthy@google.com>
---
 arch/x86/kvm/mmu/mmu.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)
diff mbox series

Patch

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 937329bee654e..a965c048edde8 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -3192,8 +3192,13 @@  static int direct_map(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
 					     fault->req_level >= it.level);
 	}
 
-	if (WARN_ON_ONCE(it.level != fault->goal_level))
+	if (WARN_ON_ONCE(it.level != fault->goal_level)) {
+		gfn_t rounded_gfn = gfn_round_for_level(fault->gfn, fault->goal_level);
+		uint64_t len = KVM_PAGES_PER_HPAGE(fault->goal_level);
+
+		kvm_populate_efault_info(vcpu, rounded_gfn, len);
 		return -EFAULT;
+	}
 
 	ret = mmu_set_spte(vcpu, fault->slot, it.sptep, ACC_ALL,
 			   base_gfn, fault->pfn, fault);