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KVM: MMU: mmio page fault support

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The idea is from Avi:

| We could cache the result of a miss in an spte by using a reserved bit, and
| checking the page fault error code (or seeing if we get an ept violation or
| ept misconfiguration), so if we get repeated mmio on a page, we don't need to
| search the slot list/tree.
| (https://lkml.org/lkml/2011/2/22/221)

When the page fault is caused by mmio, we cache the info in the shadow page
table, and also set the reserved bits in the shadow page table, so if the mmio
is caused again, we can quickly identify it and emulate it directly

Searching mmio gfn in memslots is heavy since we need to walk all memeslots, it
can be reduced by this feature, and also avoid walking guest page table for
soft mmu.

[jan: fix operator precedence issue]

Signed-off-by: Xiao Guangrong <[email protected]>
Signed-off-by: Jan Kiszka <[email protected]>
Signed-off-by: Avi Kivity <[email protected]>
This commit is contained in:
Xiao Guangrong 2011-07-12 03:33:44 +08:00 • committed by Avi Kivity
commit ce88decffd
6 changed files with 255 additions and 14 deletions
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7
virt/kvm/kvm_main.c
View file

@ -831,6 +831,13 @@ skip_lpage:
kvm_arch_commit_memory_region(kvm, mem, old, user_alloc);
/*
* If the new memory slot is created, we need to clear all
* mmio sptes.
*/
if (npages && old.base_gfn != mem->guest_phys_addr >> PAGE_SHIFT)
kvm_arch_flush_shadow(kvm);
kvm_free_physmem_slot(&old, &new);
kfree(old_memslots);