From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754023Ab3JWNas (ORCPT ); Wed, 23 Oct 2013 09:30:48 -0400 Received: from e28smtp03.in.ibm.com ([122.248.162.3]:56191 "EHLO e28smtp03.in.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754028Ab3JWNaI (ORCPT ); Wed, 23 Oct 2013 09:30:08 -0400 From: Xiao Guangrong To: gleb@redhat.com Cc: avi.kivity@gmail.com, mtosatti@redhat.com, pbonzini@redhat.com, linux-kernel@vger.kernel.org, kvm@vger.kernel.org, Xiao Guangrong Subject: [PATCH v3 13/15] KVM: MMU: locklessly write-protect the page Date: Wed, 23 Oct 2013 21:29:31 +0800 Message-Id: <1382534973-13197-14-git-send-email-xiaoguangrong@linux.vnet.ibm.com> X-Mailer: git-send-email 1.8.1.4 In-Reply-To: <1382534973-13197-1-git-send-email-xiaoguangrong@linux.vnet.ibm.com> References: <1382534973-13197-1-git-send-email-xiaoguangrong@linux.vnet.ibm.com> X-TM-AS-MML: No X-Content-Scanned: Fidelis XPS MAILER x-cbid: 13102313-3864-0000-0000-00000AB5854E Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Currently, when mark memslot dirty logged or get dirty page, we need to write-protect large guest memory, it is the heavy work, especially, we need to hold mmu-lock which is also required by vcpu to fix its page table fault and mmu-notifier when host page is being changed. In the extreme cpu / memory used guest, it becomes a scalability issue This patch introduces a way to locklessly write-protect guest memory Now, lockless rmap walk, lockless shadow page table access and lockless spte wirte-protection are ready, it is the time to implements page write-protection out of mmu-lock Signed-off-by: Xiao Guangrong --- arch/x86/include/asm/kvm_host.h | 4 --- arch/x86/kvm/mmu.c | 59 ++++++++++++++++++++++++++++++----------- arch/x86/kvm/mmu.h | 6 +++++ arch/x86/kvm/x86.c | 11 ++++---- 4 files changed, 55 insertions(+), 25 deletions(-) diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h index df9ae10..cdb6f29 100644 --- a/arch/x86/include/asm/kvm_host.h +++ b/arch/x86/include/asm/kvm_host.h @@ -793,10 +793,6 @@ void kvm_mmu_set_mask_ptes(u64 user_mask, u64 accessed_mask, u64 dirty_mask, u64 nx_mask, u64 x_mask); void kvm_mmu_reset_context(struct kvm_vcpu *vcpu); -void kvm_mmu_slot_remove_write_access(struct kvm *kvm, int slot); -void kvm_mmu_write_protect_pt_masked(struct kvm *kvm, - struct kvm_memory_slot *slot, - gfn_t gfn_offset, unsigned long mask); void kvm_mmu_zap_all(struct kvm *kvm); void kvm_mmu_invalidate_mmio_sptes(struct kvm *kvm); unsigned int kvm_mmu_calculate_mmu_pages(struct kvm *kvm); diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c index 8b96d96..d82bbec 100644 --- a/arch/x86/kvm/mmu.c +++ b/arch/x86/kvm/mmu.c @@ -1386,8 +1386,37 @@ static bool __rmap_write_protect(struct kvm *kvm, unsigned long *rmapp, return flush; } -/** - * kvm_mmu_write_protect_pt_masked - write protect selected PT level pages +static void __rmap_write_protect_lockless(u64 *sptep) +{ + u64 spte; + +retry: + /* + * Note we may partly read the sptep on 32bit host, however, we + * allow this case because: + * - we do not access the page got from the sptep. + * - cmpxchg64 can detect that case and avoid setting a wrong value + * to the sptep. + */ + spte = *rcu_dereference(sptep); + if (unlikely(!is_last_spte(spte) || !is_writable_pte(spte))) + return; + + if (likely(cmpxchg64(sptep, spte, spte & ~PT_WRITABLE_MASK) == spte)) + return; + + goto retry; +} + +static void rmap_write_protect_lockless(unsigned long *rmapp) +{ + pte_list_walk_lockless(rmapp, __rmap_write_protect_lockless); +} + +/* + * kvm_mmu_write_protect_pt_masked_lockless - write protect selected PT level + * pages out of mmu-lock. + * * @kvm: kvm instance * @slot: slot to protect * @gfn_offset: start of the BITS_PER_LONG pages we care about @@ -1396,16 +1425,17 @@ static bool __rmap_write_protect(struct kvm *kvm, unsigned long *rmapp, * Used when we do not need to care about huge page mappings: e.g. during dirty * logging we do not have any such mappings. */ -void kvm_mmu_write_protect_pt_masked(struct kvm *kvm, - struct kvm_memory_slot *slot, - gfn_t gfn_offset, unsigned long mask) +void +kvm_mmu_write_protect_pt_masked_lockless(struct kvm *kvm, + struct kvm_memory_slot *slot, + gfn_t gfn_offset, unsigned long mask) { unsigned long *rmapp; while (mask) { rmapp = __gfn_to_rmap(slot->base_gfn + gfn_offset + __ffs(mask), PT_PAGE_TABLE_LEVEL, slot); - __rmap_write_protect(kvm, rmapp, false); + rmap_write_protect_lockless(rmapp); /* clear the first set bit */ mask &= mask - 1; @@ -4477,7 +4507,7 @@ void kvm_mmu_setup(struct kvm_vcpu *vcpu) init_kvm_mmu(vcpu); } -void kvm_mmu_slot_remove_write_access(struct kvm *kvm, int slot) +void kvm_mmu_slot_remove_write_access_lockless(struct kvm *kvm, int slot) { struct kvm_memory_slot *memslot; gfn_t last_gfn; @@ -4486,8 +4516,7 @@ void kvm_mmu_slot_remove_write_access(struct kvm *kvm, int slot) memslot = id_to_memslot(kvm->memslots, slot); last_gfn = memslot->base_gfn + memslot->npages - 1; - spin_lock(&kvm->mmu_lock); - + rcu_read_lock(); for (i = PT_PAGE_TABLE_LEVEL; i < PT_PAGE_TABLE_LEVEL + KVM_NR_PAGE_SIZES; ++i) { unsigned long *rmapp; @@ -4497,15 +4526,15 @@ void kvm_mmu_slot_remove_write_access(struct kvm *kvm, int slot) last_index = gfn_to_index(last_gfn, memslot->base_gfn, i); for (index = 0; index <= last_index; ++index, ++rmapp) { - if (*rmapp) - __rmap_write_protect(kvm, rmapp, false); + rmap_write_protect_lockless(rmapp); - if (need_resched() || spin_needbreak(&kvm->mmu_lock)) - cond_resched_lock(&kvm->mmu_lock); + if (need_resched()) { + rcu_read_lock(); + rcu_read_unlock(); + } } } - - spin_unlock(&kvm->mmu_lock); + rcu_read_unlock(); /* * We can flush all the TLBs out of the mmu lock without TLB diff --git a/arch/x86/kvm/mmu.h b/arch/x86/kvm/mmu.h index 2926152..33f313b 100644 --- a/arch/x86/kvm/mmu.h +++ b/arch/x86/kvm/mmu.h @@ -117,4 +117,10 @@ static inline bool permission_fault(struct kvm_mmu *mmu, unsigned pte_access, } void kvm_mmu_invalidate_zap_all_pages(struct kvm *kvm); + +void kvm_mmu_slot_remove_write_access_lockless(struct kvm *kvm, int slot); +void +kvm_mmu_write_protect_pt_masked_lockless(struct kvm *kvm, + struct kvm_memory_slot *slot, + gfn_t gfn_offset, unsigned long mask); #endif diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 4ac3a27..c6233e1 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -3554,8 +3554,7 @@ int kvm_vm_ioctl_get_dirty_log(struct kvm *kvm, struct kvm_dirty_log *log) dirty_bitmap_buffer = dirty_bitmap + n / sizeof(long); memset(dirty_bitmap_buffer, 0, n); - spin_lock(&kvm->mmu_lock); - + rcu_read_lock(); for (i = 0; i < n / sizeof(long); i++) { unsigned long mask; gfn_t offset; @@ -3579,10 +3578,10 @@ int kvm_vm_ioctl_get_dirty_log(struct kvm *kvm, struct kvm_dirty_log *log) dirty_bitmap_buffer[i] = mask; offset = i * BITS_PER_LONG; - kvm_mmu_write_protect_pt_masked(kvm, memslot, offset, mask); + kvm_mmu_write_protect_pt_masked_lockless(kvm, memslot, + offset, mask); } - - spin_unlock(&kvm->mmu_lock); + rcu_read_unlock(); /* * All the TLBs can be flushed out of mmu lock, see the comments in @@ -7246,7 +7245,7 @@ void kvm_arch_commit_memory_region(struct kvm *kvm, * See the comments in fast_page_fault(). */ if ((change != KVM_MR_DELETE) && (mem->flags & KVM_MEM_LOG_DIRTY_PAGES)) - kvm_mmu_slot_remove_write_access(kvm, mem->slot); + kvm_mmu_slot_remove_write_access_lockless(kvm, mem->slot); } void kvm_arch_flush_shadow_all(struct kvm *kvm) -- 1.8.1.4