Commit a25f7e1f authored Apr 30, 2007 by Avi Kivity

KVM: Reduce misfirings of the fork detector

The kvm mmu tries to detects forks by looking for repeated writes to a
page table. If it sees a fork, it unshadows the page table so the page
table copying can proceed at native speed instead of being emulated.

However, the detector also triggered on simple demand paging access patterns:
a linear walk of memory would of course cause repeated writes to the same
pagetable page, causing it to unshadow prematurely.

Fix by resetting the fork detector if we detect a demand fault.

Signed-off-by: Avi Kivity <avi@qumranet.com>

parent 05e0c8c3

drivers/kvm/paging_tmpl.h

+4 −0

Original line number	Diff line number	Diff line
		@@ -421,6 +421,7 @@ static int FNAME(page_fault)(struct kvm_vcpu *vcpu, gva_t addr,
		pgprintk("%s: guest page fault\n", __FUNCTION__);
		inject_page_fault(vcpu, addr, walker.error_code);
		FNAME(release_walker)(&walker);
		vcpu->last_pt_write_count = 0; /* reset fork detector */
		return 0;
		}

		@@ -442,6 +443,9 @@ static int FNAME(page_fault)(struct kvm_vcpu *vcpu, gva_t addr,

		FNAME(release_walker)(&walker);

		if (!write_pt)
		vcpu->last_pt_write_count = 0; /* reset fork detector */

		/*
		* mmio: emulate if accessible, otherwise its a guest fault.
		*/