From: Sean Christopherson <seanjc@google.com>
To: Ben Gardon <bgardon@google.com>
Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
Paolo Bonzini <pbonzini@redhat.com>, Peter Xu <peterx@redhat.com>,
Peter Shier <pshier@google.com>,
Peter Feiner <pfeiner@google.com>,
Junaid Shahid <junaids@google.com>,
Jim Mattson <jmattson@google.com>,
Yulei Zhang <yulei.kernel@gmail.com>,
Wanpeng Li <kernellwp@gmail.com>,
Vitaly Kuznetsov <vkuznets@redhat.com>,
Xiao Guangrong <xiaoguangrong.eric@gmail.com>
Subject: Re: [PATCH 07/13] KVM: x86/mmu: Make TDP MMU root refcount atomic
Date: Wed, 31 Mar 2021 22:21:53 +0000 [thread overview]
Message-ID: <YGT2AV6lhDG5yLkW@google.com> (raw)
In-Reply-To: <20210331210841.3996155-8-bgardon@google.com>
On Wed, Mar 31, 2021, Ben Gardon wrote:
> In order to parallelize more operations for the TDP MMU, make the
> refcount on TDP MMU roots atomic, so that a future patch can allow
> multiple threads to take a reference on the root concurrently, while
> holding the MMU lock in read mode.
>
> Signed-off-by: Ben Gardon <bgardon@google.com>
> ---
...
> @@ -88,10 +88,12 @@ static struct kvm_mmu_page *tdp_mmu_next_root(struct kvm *kvm,
> next_root = list_first_entry(&kvm->arch.tdp_mmu_roots,
> typeof(*next_root), link);
>
> + while (!list_entry_is_head(next_root, &kvm->arch.tdp_mmu_roots, link) &&
> + !kvm_tdp_mmu_get_root(kvm, next_root))
> + next_root = list_next_entry(next_root, link);
> +
> if (list_entry_is_head(next_root, &kvm->arch.tdp_mmu_roots, link))
> next_root = NULL;
> - else
> - kvm_tdp_mmu_get_root(kvm, next_root);
>
> if (prev_root)
> kvm_tdp_mmu_put_root(kvm, prev_root);
> @@ -158,14 +160,13 @@ hpa_t kvm_tdp_mmu_get_vcpu_root_hpa(struct kvm_vcpu *vcpu)
>
> /* Check for an existing root before allocating a new one. */
> for_each_tdp_mmu_root(kvm, root) {
> - if (root->role.word == role.word) {
> - kvm_tdp_mmu_get_root(kvm, root);
> + if (root->role.word == role.word &&
> + kvm_tdp_mmu_get_root(kvm, root))
I'm not opposed to changing this logic while making the refcount atomic, but it
needs to be explained in the changelog. As is, the changelog makes it sound
like the patch is a pure refactoring of the type.
next prev parent reply other threads:[~2021-03-31 22:22 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-31 21:08 [PATCH 00/13] More parallel operations for the TDP MMU Ben Gardon
2021-03-31 21:08 ` [PATCH 01/13] KVM: x86/mmu: Re-add const qualifier in kvm_tdp_mmu_zap_collapsible_sptes Ben Gardon
2021-03-31 21:08 ` [PATCH 02/13] KVM: x86/mmu: Move kvm_mmu_(get|put)_root to TDP MMU Ben Gardon
2021-03-31 21:08 ` [PATCH 03/13] KVM: x86/mmu: use tdp_mmu_free_sp to free roots Ben Gardon
2021-03-31 21:08 ` [PATCH 04/13] KVM: x86/mmu: Merge TDP MMU put and free root Ben Gardon
2021-03-31 21:08 ` [PATCH 05/13] KVM: x86/mmu: comment for_each_tdp_mmu_root requires MMU write lock Ben Gardon
2021-03-31 21:08 ` [PATCH 06/13] KVM: x86/mmu: Refactor yield safe root iterator Ben Gardon
2021-03-31 21:08 ` [PATCH 07/13] KVM: x86/mmu: Make TDP MMU root refcount atomic Ben Gardon
2021-03-31 22:21 ` Sean Christopherson [this message]
2021-04-01 16:50 ` Ben Gardon
2021-03-31 21:08 ` [PATCH 08/13] KVM: x86/mmu: Protect the tdp_mmu_roots list with RCU Ben Gardon
2021-04-01 9:37 ` Paolo Bonzini
2021-04-01 16:48 ` Ben Gardon
2021-04-01 13:16 ` kernel test robot
2021-04-01 16:50 ` Ben Gardon
2021-03-31 21:08 ` [PATCH 09/13] KVM: x86/mmu: Allow zap gfn range to operate under the mmu read lock Ben Gardon
2021-04-01 9:58 ` Paolo Bonzini
2021-04-01 16:50 ` Ben Gardon
2021-03-31 21:08 ` [PATCH 10/13] KVM: x86/mmu: Allow zapping collapsible SPTEs to use MMU " Ben Gardon
2021-04-01 10:12 ` Paolo Bonzini
2021-03-31 21:08 ` [PATCH 11/13] KVM: x86/mmu: Allow enabling / disabling dirty logging under " Ben Gardon
2021-03-31 21:08 ` [PATCH 12/13] KVM: x86/mmu: Fast invalidation for TDP MMU Ben Gardon
2021-03-31 22:27 ` Sean Christopherson
2021-04-01 16:50 ` Ben Gardon
2021-04-01 10:36 ` Paolo Bonzini
2021-04-01 16:50 ` Ben Gardon
2021-04-01 17:02 ` Paolo Bonzini
2021-03-31 21:08 ` [PATCH 13/13] KVM: x86/mmu: Tear down roots in fast invalidation thread Ben Gardon
2021-03-31 22:29 ` Sean Christopherson
2021-04-01 10:41 ` Paolo Bonzini
2021-04-01 10:37 ` Paolo Bonzini
2021-04-01 10:43 ` [PATCH 00/13] More parallel operations for the TDP MMU Paolo Bonzini
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