From: Sean Christopherson <sean.j.christopherson@intel.com>
To: Ben Gardon <bgardon@google.com>
Cc: kvm@vger.kernel.org, Paolo Bonzini <pbonzini@redhat.com>,
Peter Feiner <pfeiner@google.com>,
Peter Shier <pshier@google.com>,
Junaid Shahid <junaids@google.com>,
Jim Mattson <jmattson@google.com>
Subject: Re: [RFC PATCH 04/28] kvm: mmu: Update the lpages stat atomically
Date: Wed, 27 Nov 2019 10:39:11 -0800 [thread overview]
Message-ID: <20191127183911.GD22227@linux.intel.com> (raw)
In-Reply-To: <20190926231824.149014-5-bgardon@google.com>
On Thu, Sep 26, 2019 at 04:18:00PM -0700, Ben Gardon wrote:
> In order to pave the way for more concurrent MMU operations, updates to
> VM-global stats need to be done atomically. Change updates to the lpages
> stat to be atomic in preparation for the introduction of parallel page
> fault handling.
>
> Signed-off-by: Ben Gardon <bgardon@google.com>
> ---
> arch/x86/kvm/mmu.c | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
> index 1ecd6d51c0ee0..56587655aecb9 100644
> --- a/arch/x86/kvm/mmu.c
> +++ b/arch/x86/kvm/mmu.c
> @@ -1532,7 +1532,7 @@ static bool __drop_large_spte(struct kvm *kvm, u64 *sptep)
> WARN_ON(page_header(__pa(sptep))->role.level ==
> PT_PAGE_TABLE_LEVEL);
> drop_spte(kvm, sptep);
> - --kvm->stat.lpages;
> + xadd(&kvm->stat.lpages, -1);
Manually doing atomic operations without converting the variable itself to
an atomic feels like a hack, e.g. lacks the compile time checks provided
by the atomics framework.
Tangentially related, should the members of struct kvm_vm_stat be forced
to 64-bit variables to avoid theoretical wrapping on 32-bit KVM?
> return true;
> }
>
> @@ -2676,7 +2676,7 @@ static bool mmu_page_zap_pte(struct kvm *kvm, struct kvm_mmu_page *sp,
> if (is_last_spte(pte, sp->role.level)) {
> drop_spte(kvm, spte);
> if (is_large_pte(pte))
> - --kvm->stat.lpages;
> + xadd(&kvm->stat.lpages, -1);
> } else {
> child = page_header(pte & PT64_BASE_ADDR_MASK);
> drop_parent_pte(child, spte);
> @@ -3134,7 +3134,7 @@ static int mmu_set_spte(struct kvm_vcpu *vcpu, u64 *sptep, unsigned pte_access,
> pgprintk("%s: setting spte %llx\n", __func__, *sptep);
> trace_kvm_mmu_set_spte(level, gfn, sptep);
> if (!was_rmapped && is_large_pte(*sptep))
> - ++vcpu->kvm->stat.lpages;
> + xadd(&vcpu->kvm->stat.lpages, 1);
>
> if (is_shadow_present_pte(*sptep)) {
> if (!was_rmapped) {
> --
> 2.23.0.444.g18eeb5a265-goog
>
next prev parent reply other threads:[~2019-11-27 18:39 UTC|newest]
Thread overview: 57+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-09-26 23:17 [RFC PATCH 00/28] kvm: mmu: Rework the x86 TDP direct mapped case Ben Gardon
2019-09-26 23:17 ` [RFC PATCH 01/28] kvm: mmu: Separate generating and setting mmio ptes Ben Gardon
2019-11-27 18:15 ` Sean Christopherson
2019-09-26 23:17 ` [RFC PATCH 02/28] kvm: mmu: Separate pte generation from set_spte Ben Gardon
2019-11-27 18:25 ` Sean Christopherson
2019-09-26 23:17 ` [RFC PATCH 03/28] kvm: mmu: Zero page cache memory at allocation time Ben Gardon
2019-11-27 18:32 ` Sean Christopherson
2019-09-26 23:18 ` [RFC PATCH 04/28] kvm: mmu: Update the lpages stat atomically Ben Gardon
2019-11-27 18:39 ` Sean Christopherson [this message]
2019-12-06 20:10 ` Ben Gardon
2019-09-26 23:18 ` [RFC PATCH 05/28] sched: Add cond_resched_rwlock Ben Gardon
2019-11-27 18:42 ` Sean Christopherson
2019-12-06 20:12 ` Ben Gardon
2019-09-26 23:18 ` [RFC PATCH 06/28] kvm: mmu: Replace mmu_lock with a read/write lock Ben Gardon
2019-11-27 18:47 ` Sean Christopherson
2019-12-02 22:45 ` Sean Christopherson
2019-09-26 23:18 ` [RFC PATCH 07/28] kvm: mmu: Add functions for handling changed PTEs Ben Gardon
2019-11-27 19:04 ` Sean Christopherson
2019-09-26 23:18 ` [RFC PATCH 08/28] kvm: mmu: Init / Uninit the direct MMU Ben Gardon
2019-12-02 23:40 ` Sean Christopherson
2019-12-06 20:25 ` Ben Gardon
2019-09-26 23:18 ` [RFC PATCH 09/28] kvm: mmu: Free direct MMU page table memory in an RCU callback Ben Gardon
2019-09-26 23:18 ` [RFC PATCH 10/28] kvm: mmu: Flush TLBs before freeing direct MMU page table memory Ben Gardon
2019-12-02 23:46 ` Sean Christopherson
2019-12-06 20:31 ` Ben Gardon
2019-09-26 23:18 ` [RFC PATCH 11/28] kvm: mmu: Optimize for freeing direct MMU PTs on teardown Ben Gardon
2019-12-02 23:54 ` Sean Christopherson
2019-09-26 23:18 ` [RFC PATCH 12/28] kvm: mmu: Set tlbs_dirty atomically Ben Gardon
2019-12-03 0:13 ` Sean Christopherson
2019-09-26 23:18 ` [RFC PATCH 13/28] kvm: mmu: Add an iterator for concurrent paging structure walks Ben Gardon
2019-12-03 2:15 ` Sean Christopherson
2019-12-18 18:25 ` Ben Gardon
2019-12-18 19:14 ` Sean Christopherson
2019-09-26 23:18 ` [RFC PATCH 14/28] kvm: mmu: Batch updates to the direct mmu disconnected list Ben Gardon
2019-09-26 23:18 ` [RFC PATCH 15/28] kvm: mmu: Support invalidate_zap_all_pages Ben Gardon
2019-09-26 23:18 ` [RFC PATCH 16/28] kvm: mmu: Add direct MMU page fault handler Ben Gardon
2020-01-08 17:20 ` Peter Xu
2020-01-08 18:15 ` Ben Gardon
2020-01-08 19:00 ` Peter Xu
2019-09-26 23:18 ` [RFC PATCH 17/28] kvm: mmu: Add direct MMU fast " Ben Gardon
2019-09-26 23:18 ` [RFC PATCH 18/28] kvm: mmu: Add an hva range iterator for memslot GFNs Ben Gardon
2019-09-26 23:18 ` [RFC PATCH 19/28] kvm: mmu: Make address space ID a property of memslots Ben Gardon
2019-09-26 23:18 ` [RFC PATCH 20/28] kvm: mmu: Implement the invalidation MMU notifiers for the direct MMU Ben Gardon
2019-09-26 23:18 ` [RFC PATCH 21/28] kvm: mmu: Integrate the direct mmu with the changed pte notifier Ben Gardon
2019-09-26 23:18 ` [RFC PATCH 22/28] kvm: mmu: Implement access tracking for the direct MMU Ben Gardon
2019-09-26 23:18 ` [RFC PATCH 23/28] kvm: mmu: Make mark_page_dirty_in_slot usable from outside kvm_main Ben Gardon
2019-09-26 23:18 ` [RFC PATCH 24/28] kvm: mmu: Support dirty logging in the direct MMU Ben Gardon
2019-09-26 23:18 ` [RFC PATCH 25/28] kvm: mmu: Support kvm_zap_gfn_range " Ben Gardon
2019-09-26 23:18 ` [RFC PATCH 26/28] kvm: mmu: Integrate direct MMU with nesting Ben Gardon
2019-09-26 23:18 ` [RFC PATCH 27/28] kvm: mmu: Lazily allocate rmap when direct MMU is enabled Ben Gardon
2019-09-26 23:18 ` [RFC PATCH 28/28] kvm: mmu: Support MMIO in the direct MMU Ben Gardon
2019-10-17 18:50 ` [RFC PATCH 00/28] kvm: mmu: Rework the x86 TDP direct mapped case Sean Christopherson
2019-10-18 13:42 ` Paolo Bonzini
2019-11-27 19:09 ` Sean Christopherson
2019-12-06 19:55 ` Ben Gardon
2019-12-06 19:57 ` Sean Christopherson
2019-12-06 20:42 ` Ben Gardon
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