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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>
This commit is contained in:
Avi Kivity 2007-04-30 17:05:38 +03:00
parent 05e0c8c344
commit a25f7e1f8c
1 changed files with 4 additions and 0 deletions
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4
drivers/kvm/paging_tmpl.h
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@ -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.
*/