| Message ID | 20211124214421.458549-2-mizhang@google.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | optimize spte zapping in zap_gfn_range() | expand |
On Wed, Nov 24, 2021 at 09:44:20PM +0000, Mingwei Zhang wrote: > Not stepping down in TDP iterator in `zap_all` case avoids re-reading the > non-leaf SPTEs, thus accelerates the zapping process . But when the number > of SPTEs is too large, we may run out of CPU time and causes a RCU stall > warnings in __handle_changed_pte() in the context of zap_gfn_range(). > > Revert this patch to allow eliminating RCU stall warning using a two-phase > zapping for `zap_all` case. > > This reverts commit 0103098fb4f13b447b26ed514bcd3140f6791047. > > Cc: Sean Christopherson <seanjc@google.com> > Cc: Ben Gardon <bgardon@google.com> > Cc: David Matlack <dmatlack@google.com> > > Signed-off-by: Mingwei Zhang <mizhang@google.com> Reviewed-by: David Matlack <dmatlack@google.com> > --- > arch/x86/kvm/mmu/tdp_mmu.c | 9 +-------- > 1 file changed, 1 insertion(+), 8 deletions(-) > > diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c > index 7c5dd83e52de..89d16bb104de 100644 > --- a/arch/x86/kvm/mmu/tdp_mmu.c > +++ b/arch/x86/kvm/mmu/tdp_mmu.c > @@ -706,12 +706,6 @@ static bool zap_gfn_range(struct kvm *kvm, struct kvm_mmu_page *root, > bool zap_all = (start == 0 && end >= max_gfn_host); > struct tdp_iter iter; > > - /* > - * No need to try to step down in the iterator when zapping all SPTEs, > - * zapping the top-level non-leaf SPTEs will recurse on their children. > - */ > - int min_level = zap_all ? root->role.level : PG_LEVEL_4K; > - > /* > * Bound the walk at host.MAXPHYADDR, guest accesses beyond that will > * hit a #PF(RSVD) and never get to an EPT Violation/Misconfig / #NPF, > @@ -723,8 +717,7 @@ static bool zap_gfn_range(struct kvm *kvm, struct kvm_mmu_page *root, > > rcu_read_lock(); > > - for_each_tdp_pte_min_level(iter, root->spt, root->role.level, > - min_level, start, end) { > + tdp_root_for_each_pte(iter, root, start, end) { > retry: > if (can_yield && > tdp_mmu_iter_cond_resched(kvm, &iter, flush, shared)) { > -- > 2.34.0.rc2.393.gf8c9666880-goog >
diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c index 7c5dd83e52de..89d16bb104de 100644 --- a/arch/x86/kvm/mmu/tdp_mmu.c +++ b/arch/x86/kvm/mmu/tdp_mmu.c @@ -706,12 +706,6 @@ static bool zap_gfn_range(struct kvm *kvm, struct kvm_mmu_page *root, bool zap_all = (start == 0 && end >= max_gfn_host); struct tdp_iter iter; - /* - * No need to try to step down in the iterator when zapping all SPTEs, - * zapping the top-level non-leaf SPTEs will recurse on their children. - */ - int min_level = zap_all ? root->role.level : PG_LEVEL_4K; - /* * Bound the walk at host.MAXPHYADDR, guest accesses beyond that will * hit a #PF(RSVD) and never get to an EPT Violation/Misconfig / #NPF, @@ -723,8 +717,7 @@ static bool zap_gfn_range(struct kvm *kvm, struct kvm_mmu_page *root, rcu_read_lock(); - for_each_tdp_pte_min_level(iter, root->spt, root->role.level, - min_level, start, end) { + tdp_root_for_each_pte(iter, root, start, end) { retry: if (can_yield && tdp_mmu_iter_cond_resched(kvm, &iter, flush, shared)) {
Not stepping down in TDP iterator in `zap_all` case avoids re-reading the non-leaf SPTEs, thus accelerates the zapping process . But when the number of SPTEs is too large, we may run out of CPU time and causes a RCU stall warnings in __handle_changed_pte() in the context of zap_gfn_range(). Revert this patch to allow eliminating RCU stall warning using a two-phase zapping for `zap_all` case. This reverts commit 0103098fb4f13b447b26ed514bcd3140f6791047. Cc: Sean Christopherson <seanjc@google.com> Cc: Ben Gardon <bgardon@google.com> Cc: David Matlack <dmatlack@google.com> Signed-off-by: Mingwei Zhang <mizhang@google.com> --- arch/x86/kvm/mmu/tdp_mmu.c | 9 +-------- 1 file changed, 1 insertion(+), 8 deletions(-)