linux-kernel - Re: [Patch v4 03/18] KVM: x86/mmu: Track count of pages in KVM MMU page caches globally

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Message-ID: <ZAp4Tb8MYoggn/Rb@google.com>
Date:   Thu, 9 Mar 2023 16:22:37 -0800
From:   David Matlack <dmatlack@...gle.com>
To:     Vipin Sharma <vipinsh@...gle.com>
Cc:     seanjc@...gle.com, pbonzini@...hat.com, bgardon@...gle.com,
        jmattson@...gle.com, mizhang@...gle.com, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [Patch v4 03/18] KVM: x86/mmu: Track count of pages in KVM MMU
 page caches globally

On Mon, Mar 06, 2023 at 02:41:12PM -0800, Vipin Sharma wrote:
>
>  static void mmu_free_memory_caches(struct kvm_vcpu *vcpu)
>  {
>  	kvm_mmu_free_memory_cache(&vcpu->arch.mmu_pte_list_desc_cache);
> -	kvm_mmu_free_memory_cache(&vcpu->arch.mmu_shadow_page_cache);
> +	mutex_lock(&vcpu->arch.mmu_shadow_page_cache_lock);
> +	mmu_free_sp_memory_cache(&vcpu->arch.mmu_shadow_page_cache);
> +	mutex_unlock(&vcpu->arch.mmu_shadow_page_cache_lock);

Is this lock necessary (even when the shrinker is hooked up)?
mmu_free_memory_caches() is only called when KVM fails to create a vCPU
(before it has been added to vcpu_array) or during VM destruction (after
the VM has been removed from vm_list).