Commit 1c118b82 authored Jul 18, 2013 by Xiao Guangrong Committed by Paolo Bonzini Jul 18, 2013

KVM: MMU: avoid fast page fault fixing mmio page fault



Currently, fast page fault incorrectly tries to fix mmio page fault when
the generation number is invalid (spte.gen != kvm.gen).  It then returns
to guest to retry the fault since it sees the last spte is nonpresent.
This causes an infinite loop.

Since fast page fault only works for direct mmu, the issue exists when
1) tdp is enabled. It is only triggered only on AMD host since on Intel host
   the mmio page fault is recognized as ept-misconfig whose handler call
   fault-page path with error_code = 0

2) guest paging is disabled. Under this case, the issue is hardly discovered
   since paging disable is short-lived and the sptes will be invalid after
   memslot changed for 150 times

Fix it by filtering out MMIO page faults in page_fault_can_be_fast.

Reported-by: Markus Trippelsdorf <markus@trippelsdorf.de>
Tested-by: Markus Trippelsdorf <markus@trippelsdorf.de>
Signed-off-by: Xiao Guangrong <xiaoguangrong@linux.vnet.ibm.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

parent ad81f054

arch/x86/kvm/mmu.c

+7 −0

Original line number	Diff line number	Diff line
		@@ -2810,6 +2810,13 @@ exit:

		static bool page_fault_can_be_fast(struct kvm_vcpu *vcpu, u32 error_code)
		{
		/*
		* Do not fix the mmio spte with invalid generation number which
		* need to be updated by slow page fault path.
		*/
		if (unlikely(error_code & PFERR_RSVD_MASK))
		return false;

		/*
		* #PF can be fast only if the shadow page table is present and it
		* is caused by write-protect, that means we just need change the

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