From: Paolo Bonzini <pbonzini@redhat.com>
To: Sean Christopherson <sean.j.christopherson@intel.com>,
Ben Gardon <bgardon@google.com>
Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
Cannon Matthews <cannonmatthews@google.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 04/22] kvm: mmu: Allocate and free TDP MMU roots
Date: Wed, 30 Sep 2020 08:26:28 +0200 [thread overview]
Message-ID: <6a5b78f8-0fbe-fbec-8313-f7759e2483b0@redhat.com> (raw)
In-Reply-To: <20200930060610.GA29659@linux.intel.com>
On 30/09/20 08:06, Sean Christopherson wrote:
>> +static struct kvm_mmu_page *alloc_tdp_mmu_root(struct kvm_vcpu *vcpu,
>> + union kvm_mmu_page_role role)
>> +{
>> + struct kvm_mmu_page *new_root;
>> + struct kvm_mmu_page *root;
>> +
>> + new_root = kvm_mmu_memory_cache_alloc(
>> + &vcpu->arch.mmu_page_header_cache);
>> + new_root->spt = kvm_mmu_memory_cache_alloc(
>> + &vcpu->arch.mmu_shadow_page_cache);
>> + set_page_private(virt_to_page(new_root->spt), (unsigned long)new_root);
>> +
>> + new_root->role.word = role.word;
>> + new_root->root_count = 1;
>> + new_root->gfn = 0;
>> + new_root->tdp_mmu_page = true;
>> +
>> + spin_lock(&vcpu->kvm->mmu_lock);
>> +
>> + /* Check that no matching root exists before adding this one. */
>> + root = find_tdp_mmu_root_with_role(vcpu->kvm, role);
>> + if (root) {
>> + get_tdp_mmu_root(vcpu->kvm, root);
>> + spin_unlock(&vcpu->kvm->mmu_lock);
> Hrm, I'm not a big fan of dropping locks in the middle of functions, but the
> alternatives aren't great. :-/ Best I can come up with is
>
> if (root)
> get_tdp_mmu_root()
> else
> list_add();
>
> spin_unlock();
>
> if (root) {
> free_page()
> kmem_cache_free()
> } else {
> root = new_root;
> }
>
> return root;
>
> Not sure that's any better.
>
>> + free_page((unsigned long)new_root->spt);
>> + kmem_cache_free(mmu_page_header_cache, new_root);
>> + return root;
>> + }
>> +
>> + list_add(&new_root->link, &vcpu->kvm->arch.tdp_mmu_roots);
>> + spin_unlock(&vcpu->kvm->mmu_lock);
>> +
>> + return new_root;
>> +}
>> +
>> +static struct kvm_mmu_page *get_tdp_mmu_vcpu_root(struct kvm_vcpu *vcpu)
>> +{
>> + struct kvm_mmu_page *root;
>> + union kvm_mmu_page_role role;
>> +
>> + role = vcpu->arch.mmu->mmu_role.base;
>> + role.level = vcpu->arch.mmu->shadow_root_level;
>> + role.direct = true;
>> + role.gpte_is_8_bytes = true;
>> + role.access = ACC_ALL;
>> +
>> + spin_lock(&vcpu->kvm->mmu_lock);
>> +
>> + /* Search for an already allocated root with the same role. */
>> + root = find_tdp_mmu_root_with_role(vcpu->kvm, role);
>> + if (root) {
>> + get_tdp_mmu_root(vcpu->kvm, root);
>> + spin_unlock(&vcpu->kvm->mmu_lock);
> Rather than manually unlock and return, this can be
>
> if (root)
> get_tdp_mmju_root();
>
> spin_unlock()
>
> if (!root)
> root = alloc_tdp_mmu_root();
>
> return root;
>
> You could also add a helper to do the "get" along with the "find". Not sure
> if that's worth the code.
All in all I don't think it's any clearer than Ben's code. At least in
his case the "if"s clearly point at the double-checked locking pattern.
Paolo
next prev parent reply other threads:[~2020-09-30 6:26 UTC|newest]
Thread overview: 105+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-25 21:22 [PATCH 00/22] Introduce the TDP MMU Ben Gardon
2020-09-25 21:22 ` [PATCH 01/22] kvm: mmu: Separate making SPTEs from set_spte Ben Gardon
2020-09-30 4:55 ` Sean Christopherson
2020-09-30 23:03 ` Ben Gardon
2020-09-25 21:22 ` [PATCH 02/22] kvm: mmu: Introduce tdp_iter Ben Gardon
2020-09-26 0:04 ` Paolo Bonzini
2020-09-30 5:06 ` Sean Christopherson
2020-09-26 0:54 ` Paolo Bonzini
2020-09-30 5:08 ` Sean Christopherson
2020-09-30 5:24 ` Sean Christopherson
2020-09-30 6:24 ` Paolo Bonzini
2020-09-30 23:20 ` Eric van Tassell
2020-09-30 23:34 ` Paolo Bonzini
2020-10-01 0:07 ` Sean Christopherson
2020-09-25 21:22 ` [PATCH 03/22] kvm: mmu: Init / Uninit the TDP MMU Ben Gardon
2020-09-26 0:06 ` Paolo Bonzini
2020-09-30 5:34 ` Sean Christopherson
2020-09-30 18:36 ` Ben Gardon
2020-09-30 16:57 ` Sean Christopherson
2020-09-30 17:39 ` Paolo Bonzini
2020-09-30 18:42 ` Ben Gardon
2020-09-25 21:22 ` [PATCH 04/22] kvm: mmu: Allocate and free TDP MMU roots Ben Gardon
2020-09-30 6:06 ` Sean Christopherson
2020-09-30 6:26 ` Paolo Bonzini [this message]
2020-09-30 15:38 ` Sean Christopherson
2020-10-12 22:59 ` Ben Gardon
2020-10-12 23:59 ` Sean Christopherson
2020-09-25 21:22 ` [PATCH 05/22] kvm: mmu: Add functions to handle changed TDP SPTEs Ben Gardon
2020-09-26 0:39 ` Paolo Bonzini
2020-09-28 17:23 ` Paolo Bonzini
2020-09-25 21:22 ` [PATCH 06/22] kvm: mmu: Make address space ID a property of memslots Ben Gardon
2020-09-30 6:10 ` Sean Christopherson
2020-09-30 23:11 ` Ben Gardon
2020-09-25 21:22 ` [PATCH 07/22] kvm: mmu: Support zapping SPTEs in the TDP MMU Ben Gardon
2020-09-26 0:14 ` Paolo Bonzini
2020-09-30 6:15 ` Sean Christopherson
2020-09-30 6:28 ` Paolo Bonzini
2020-09-25 21:22 ` [PATCH 08/22] kvm: mmu: Separate making non-leaf sptes from link_shadow_page Ben Gardon
2020-09-25 21:22 ` [PATCH 09/22] kvm: mmu: Remove disallowed_hugepage_adjust shadow_walk_iterator arg Ben Gardon
2020-09-30 16:19 ` Sean Christopherson
2020-09-25 21:22 ` [PATCH 10/22] kvm: mmu: Add TDP MMU PF handler Ben Gardon
2020-09-26 0:24 ` Paolo Bonzini
2020-09-30 16:37 ` Sean Christopherson
2020-09-30 16:55 ` Paolo Bonzini
2020-09-30 17:37 ` Paolo Bonzini
2020-10-06 22:35 ` Ben Gardon
2020-10-06 22:33 ` Ben Gardon
2020-10-07 20:55 ` Sean Christopherson
2020-09-25 21:22 ` [PATCH 11/22] kvm: mmu: Factor out allocating a new tdp_mmu_page Ben Gardon
2020-09-26 0:22 ` Paolo Bonzini
2020-09-30 18:53 ` Ben Gardon
2020-09-25 21:22 ` [PATCH 12/22] kvm: mmu: Allocate struct kvm_mmu_pages for all pages in TDP MMU Ben Gardon
2020-09-25 21:22 ` [PATCH 13/22] kvm: mmu: Support invalidate range MMU notifier for " Ben Gardon
2020-09-30 17:03 ` Sean Christopherson
2020-09-30 23:15 ` Ben Gardon
2020-09-30 23:24 ` Sean Christopherson
2020-09-30 23:27 ` Ben Gardon
2020-09-25 21:22 ` [PATCH 14/22] kvm: mmu: Add access tracking for tdp_mmu Ben Gardon
2020-09-26 0:32 ` Paolo Bonzini
2020-09-30 17:48 ` Sean Christopherson
2020-10-06 23:38 ` Ben Gardon
2020-09-25 21:22 ` [PATCH 15/22] kvm: mmu: Support changed pte notifier in tdp MMU Ben Gardon
2020-09-26 0:33 ` Paolo Bonzini
2020-09-28 15:11 ` Paolo Bonzini
2020-10-07 16:53 ` Ben Gardon
2020-10-07 17:18 ` Paolo Bonzini
2020-10-07 17:30 ` Ben Gardon
2020-10-07 17:54 ` Paolo Bonzini
2020-09-25 21:22 ` [PATCH 16/22] kvm: mmu: Add dirty logging handler for changed sptes Ben Gardon
2020-09-26 0:45 ` Paolo Bonzini
2020-09-25 21:22 ` [PATCH 17/22] kvm: mmu: Support dirty logging for the TDP MMU Ben Gardon
2020-09-26 1:04 ` Paolo Bonzini
2020-10-08 18:27 ` Ben Gardon
2020-09-29 15:07 ` Paolo Bonzini
2020-09-30 18:04 ` Sean Christopherson
2020-09-30 18:08 ` Paolo Bonzini
2020-09-25 21:22 ` [PATCH 18/22] kvm: mmu: Support disabling dirty logging for the tdp MMU Ben Gardon
2020-09-26 1:09 ` Paolo Bonzini
2020-10-07 16:30 ` Ben Gardon
2020-10-07 17:21 ` Paolo Bonzini
2020-10-07 17:28 ` Ben Gardon
2020-10-07 17:53 ` Paolo Bonzini
2020-09-25 21:22 ` [PATCH 19/22] kvm: mmu: Support write protection for nesting in " Ben Gardon
2020-09-30 18:06 ` Sean Christopherson
2020-09-25 21:23 ` [PATCH 20/22] kvm: mmu: NX largepage recovery for TDP MMU Ben Gardon
2020-09-26 1:14 ` Paolo Bonzini
2020-09-30 22:23 ` Ben Gardon
2020-09-29 18:24 ` Paolo Bonzini
2020-09-30 18:15 ` Sean Christopherson
2020-09-30 19:56 ` Paolo Bonzini
2020-09-30 22:33 ` Ben Gardon
2020-09-30 22:27 ` Ben Gardon
2020-09-25 21:23 ` [PATCH 21/22] kvm: mmu: Support MMIO in the " Ben Gardon
2020-09-30 18:19 ` Sean Christopherson
2020-09-25 21:23 ` [PATCH 22/22] kvm: mmu: Don't clear write flooding count for direct roots Ben Gardon
2020-09-26 1:25 ` Paolo Bonzini
2020-10-05 22:48 ` Ben Gardon
2020-10-05 23:44 ` Sean Christopherson
2020-10-06 16:19 ` Ben Gardon
2020-09-26 1:14 ` [PATCH 00/22] Introduce the TDP MMU Paolo Bonzini
2020-09-28 17:31 ` Paolo Bonzini
2020-09-29 17:40 ` Ben Gardon
2020-09-29 18:10 ` Paolo Bonzini
2020-09-30 6:19 ` Sean Christopherson
2020-09-30 6:30 ` Paolo Bonzini
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