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KVM: MMU: limit rmap chain length 

Otherwise the host can spend too long traversing an rmap chain, which
happens under a spinlock.

Cc: stable@kernel.org
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Avi Kivity <avi@redhat.com>
This commit is contained in:
Marcelo Tosatti 2009-08-05 15:43:58 -03:00 committed by Avi Kivity
parent e9cbde8c15
commit 53a27b39ff
1 changed files with 28 additions and 5 deletions
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33
arch/x86/kvm/mmu.c
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@ -489,16 +489,20 @@ static unsigned long *gfn_to_rmap(struct kvm *kvm, gfn_t gfn, int lpage)
*
* If rmapp bit zero is one, (then rmap & ~1) points to a struct kvm_rmap_desc
* containing more mappings.
*
* Returns the number of rmap entries before the spte was added or zero if
* the spte was not added.
*
*/
static void rmap_add(struct kvm_vcpu *vcpu, u64 *spte, gfn_t gfn, int lpage)
static int rmap_add(struct kvm_vcpu *vcpu, u64 *spte, gfn_t gfn, int lpage)
{
struct kvm_mmu_page *sp;
struct kvm_rmap_desc *desc;
unsigned long *rmapp;
int i;
int i, count = 0;
if (!is_rmap_pte(*spte))
return;
return count;
gfn = unalias_gfn(vcpu->kvm, gfn);
sp = page_header(__pa(spte));
sp->gfns[spte - sp->spt] = gfn;
@ -515,8 +519,10 @@ static void rmap_add(struct kvm_vcpu *vcpu, u64 *spte, gfn_t gfn, int lpage)
} else {
rmap_printk("rmap_add: %p %llx many->many\n", spte, *spte);
desc = (struct kvm_rmap_desc *)(*rmapp & ~1ul);
while (desc->shadow_ptes[RMAP_EXT-1] && desc->more)
while (desc->shadow_ptes[RMAP_EXT-1] && desc->more) {
desc = desc->more;
count += RMAP_EXT;
}
if (desc->shadow_ptes[RMAP_EXT-1]) {
desc->more = mmu_alloc_rmap_desc(vcpu);
desc = desc->more;
@ -525,6 +531,7 @@ static void rmap_add(struct kvm_vcpu *vcpu, u64 *spte, gfn_t gfn, int lpage)
;
desc->shadow_ptes[i] = spte;
}
return count;
}
static void rmap_desc_remove_entry(unsigned long *rmapp,
@ -754,6 +761,19 @@ static int kvm_age_rmapp(struct kvm *kvm, unsigned long *rmapp)
return young;
}
#define RMAP_RECYCLE_THRESHOLD 1000
static void rmap_recycle(struct kvm_vcpu *vcpu, gfn_t gfn, int lpage)
{
unsigned long *rmapp;
gfn = unalias_gfn(vcpu->kvm, gfn);
rmapp = gfn_to_rmap(vcpu->kvm, gfn, lpage);
kvm_unmap_rmapp(vcpu->kvm, rmapp);
kvm_flush_remote_tlbs(vcpu->kvm);
}
int kvm_age_hva(struct kvm *kvm, unsigned long hva)
{
return kvm_handle_hva(kvm, hva, kvm_age_rmapp);
@ -1741,6 +1761,7 @@ static void mmu_set_spte(struct kvm_vcpu *vcpu, u64 *shadow_pte,
{
int was_rmapped = 0;
int was_writeble = is_writeble_pte(*shadow_pte);
int rmap_count;
pgprintk("%s: spte %llx access %x write_fault %d"
" user_fault %d gfn %lx\n",
@ -1782,9 +1803,11 @@ static void mmu_set_spte(struct kvm_vcpu *vcpu, u64 *shadow_pte,
page_header_update_slot(vcpu->kvm, shadow_pte, gfn);
if (!was_rmapped) {
rmap_add(vcpu, shadow_pte, gfn, largepage);
rmap_count = rmap_add(vcpu, shadow_pte, gfn, largepage);
if (!is_rmap_pte(*shadow_pte))
kvm_release_pfn_clean(pfn);
if (rmap_count > RMAP_RECYCLE_THRESHOLD)
rmap_recycle(vcpu, gfn, largepage);
} else {
if (was_writeble)
kvm_release_pfn_dirty(pfn);