diff options
| author | Avi Kivity <avi@qumranet.com> | 2007-01-05 16:36:50 -0800 |
|---|---|---|
| committer | Linus Torvalds <torvalds@woody.osdl.org> | 2007-01-05 23:55:26 -0800 |
| commit | 86a5ba025d0a0b251817d0efbeaf7037d4175d21 (patch) | |
| tree | 35dbc71edaa0d242ba4c0ca429c41cff67df38d0 /drivers/kvm/mmu.c | |
| parent | 139bdb2d9e410d448281057a37b53770324ccac8 (diff) | |
| download | linux-86a5ba025d0a0b251817d0efbeaf7037d4175d21.tar.bz2 | |
[PATCH] KVM: MMU: Page table write flood protection
In fork() (or when we protect a page that is no longer a page table), we can
experience floods of writes to a page, which have to be emulated. This is
expensive.
So, if we detect such a flood, zap the page so subsequent writes can proceed
natively.
Signed-off-by: Avi Kivity <avi@qumranet.com>
Acked-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Diffstat (limited to 'drivers/kvm/mmu.c')
| -rw-r--r-- | drivers/kvm/mmu.c | 16 |
1 files changed, 15 insertions, 1 deletions
diff --git a/drivers/kvm/mmu.c b/drivers/kvm/mmu.c index 8cf3688f7e70..0e44aca9eee7 100644 --- a/drivers/kvm/mmu.c +++ b/drivers/kvm/mmu.c @@ -969,8 +969,17 @@ void kvm_mmu_pre_write(struct kvm_vcpu *vcpu, gpa_t gpa, int bytes) unsigned page_offset; unsigned misaligned; int level; + int flooded = 0; pgprintk("%s: gpa %llx bytes %d\n", __FUNCTION__, gpa, bytes); + if (gfn == vcpu->last_pt_write_gfn) { + ++vcpu->last_pt_write_count; + if (vcpu->last_pt_write_count >= 3) + flooded = 1; + } else { + vcpu->last_pt_write_gfn = gfn; + vcpu->last_pt_write_count = 1; + } index = kvm_page_table_hashfn(gfn) % KVM_NUM_MMU_PAGES; bucket = &vcpu->kvm->mmu_page_hash[index]; hlist_for_each_entry_safe(page, node, n, bucket, hash_link) { @@ -978,11 +987,16 @@ void kvm_mmu_pre_write(struct kvm_vcpu *vcpu, gpa_t gpa, int bytes) continue; pte_size = page->role.glevels == PT32_ROOT_LEVEL ? 4 : 8; misaligned = (offset ^ (offset + bytes - 1)) & ~(pte_size - 1); - if (misaligned) { + if (misaligned || flooded) { /* * Misaligned accesses are too much trouble to fix * up; also, they usually indicate a page is not used * as a page table. + * + * If we're seeing too many writes to a page, + * it may no longer be a page table, or we may be + * forking, in which case it is better to unmap the + * page. */ pgprintk("misaligned: gpa %llx bytes %d role %x\n", gpa, bytes, page->role.word); |