From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pf1-f172.google.com (mail-pf1-f172.google.com [209.85.210.172]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 80EC01A276 for ; Tue, 1 Oct 2024 22:17:04 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.210.172 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1727821026; cv=none; b=EtLbU11admnOVa+Unh/f9fhMCvu7vWCSDHWqgg20F3TDd1UMcE645aS4i7p9dzL6FovKUfMkc9O4FIi76XcxEFD96GU2GWsIuOaqO4I0e2txZOjA7RO2N1uSyHF03VReLo0MMjmuJv/XDxz3zaPckAPTKT8Fj90atO8I5keQDXs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1727821026; c=relaxed/simple; bh=aUycHbqaI1GxiTXNAuLFzydIxxDE2ASlSYxOxFOpKmY=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=NDzEHlS9P2562SxWmwqvk0QcxN3sI/mQA83JjEWp7+o5X5eFlhulqI6W9ywep2BBVXWD40Y1Oif/EiHUjrsOGfiqmwkXojNxfcIh3zmSNnGUN4ZelxFD/yFrSk8kSOKUqmh7u4pZAHMekaJaE+eW9vtdWsfZXSOFXq2RVZdDgrg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=IEF0QXML; arc=none smtp.client-ip=209.85.210.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="IEF0QXML" Received: by mail-pf1-f172.google.com with SMTP id d2e1a72fcca58-71db62281aeso204526b3a.0 for ; Tue, 01 Oct 2024 15:17:04 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1727821024; x=1728425824; darn=vger.kernel.org; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:from:to:cc:subject:date:message-id:reply-to; bh=FSwzDsaIMy9+ZyD0fmi1eb2qHMifMlGySR6mVsA4DyE=; b=IEF0QXML//ylGfHiiEuQ7h2LzUOoWk4YxR3HjuyFPk1VicoDkO11pxSwG7wdbM+w1t HfxGJ7tFz6TjQUetgI+uZ+GCiRKoyzdwBQd2p99imJ6COYVKB1kOVBL/Vru3Z/d1CXRk O+SRST87cYxzymV/AiiE/e3ZlHOAXfOz+Z6RCWjbBI3fDASy07HiArv0wz9gX3o+gDxl LlaOXhmBpFyyFz1iBxB9Ia21s59nDMUqJkVXssF2iyLbZoNXOu0CUBuQO4XUbpzSl8QR dJQl1nvI39Jjp/o3yegYYq+UbRLJu3jKS94v5ZU61SmGbmvrLSrVQpzjs3rqoTNv8INb 3eEQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1727821024; x=1728425824; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to; bh=FSwzDsaIMy9+ZyD0fmi1eb2qHMifMlGySR6mVsA4DyE=; b=CRGfqABLTCBgoc4Vn44bw9V1XaledYyiFydCRH1wP0jMXmLRp+W5bbhQpjOFf8K4cY RR3vttTmy11gLhEBX6s0iY1kGVWj56cWGjeV2wafKe4dUB7/OjbRZf90hF4kO+3+c/Zb 09zdUxqLYRcjHq4ue53qXhGQMmNkFTeCEkqNdtbYCvbeIRDkn+y35zVm2AnFN7H9a96u 3EYEOPlr1B06l/Yz0MjIRGFk4jBtjHBaD43XahVBI2fEgyXr3kT25FUIlOAvxNPSbYWO A0ezc+aDdxGnDA4qoaY/Ou7MuaK9jXn/8LEwrfa7ob3Zga4VuQ4+83atCNAX+fyYd6TV v7bw== X-Forwarded-Encrypted: i=1; AJvYcCWLO9a0NXnFNVjsRH6wV47pSW8OUeJIdP+jAwPC/g+RE5EZtLEWqJ0qrI2a2JKFSV9dTO/aGse5Gjt87tE=@vger.kernel.org X-Gm-Message-State: AOJu0YzC3srL2IHV73S6bc0ukJKFxt01YfwkImktwhrvwSAlZON4wnnO PUWC9gv3Utd9CVeGGnBDmoDvxMAVH+dXsGWeLSlzxrj85dOhXbdvCPWHLvg8Eg== X-Google-Smtp-Source: AGHT+IEwweHTjwunyGCO7vEqdEao2XuJo6kPSMJhifYwsVemZvbeHHj398MLBV6ASijYoj8B0VDfYg== X-Received: by 2002:a05:6a00:66cc:b0:717:98e7:3d0 with SMTP id d2e1a72fcca58-71db787e996mr8161121b3a.0.1727821023427; Tue, 01 Oct 2024 15:17:03 -0700 (PDT) Received: from google.com (46.242.125.34.bc.googleusercontent.com. [34.125.242.46]) by smtp.gmail.com with ESMTPSA id d2e1a72fcca58-71b26518a2asm8617710b3a.107.2024.10.01.15.17.01 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 01 Oct 2024 15:17:02 -0700 (PDT) Date: Tue, 1 Oct 2024 15:16:58 -0700 From: David Matlack To: Vipin Sharma Cc: seanjc@google.com, pbonzini@redhat.com, zhi.wang.linux@gmail.com, weijiang.yang@intel.com, mizhang@google.com, liangchen.linux@gmail.com, kvm@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 2/2] KVM: x86/mmu: Use MMU shrinker to shrink KVM MMU memory caches Message-ID: References: <20240913214316.1945951-1-vipinsh@google.com> <20240913214316.1945951-3-vipinsh@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20240913214316.1945951-3-vipinsh@google.com> On 2024-09-13 02:43 PM, Vipin Sharma wrote: > Use MMU shrinker to iterate through all the vCPUs of all the VMs and > free pages allocated in MMU memory caches. Protect cache allocation in > page fault and MMU load path from MMU shrinker by using a per vCPU > mutex. In MMU shrinker, move the iterated VM to the end of the VMs list > so that the pain of emptying cache spread among other VMs too. > > The specific caches to empty are mmu_shadow_page_cache and > mmu_shadowed_info_cache as these caches store whole pages. Emptying them > will give more impact to shrinker compared to other caches like > mmu_pte_list_desc_cache{} and mmu_page_header_cache{} > > Holding per vCPU mutex lock ensures that a vCPU doesn't get surprised > by finding its cache emptied after filling them up for page table > allocations during page fault handling and MMU load operation. Per vCPU > mutex also makes sure there is only race between MMU shrinker and all > other vCPUs. This should result in very less contention. > > Suggested-by: Sean Christopherson > Suggested-by: David Matlack > Signed-off-by: Vipin Sharma > --- > arch/x86/include/asm/kvm_host.h | 6 +++ > arch/x86/kvm/mmu/mmu.c | 69 +++++++++++++++++++++++++++------ > arch/x86/kvm/mmu/paging_tmpl.h | 14 ++++--- > include/linux/kvm_host.h | 1 + > virt/kvm/kvm_main.c | 8 +++- > 5 files changed, 81 insertions(+), 17 deletions(-) > > diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h > index cbfe31bac6cf..63eaf03111eb 100644 > --- a/arch/x86/include/asm/kvm_host.h > +++ b/arch/x86/include/asm/kvm_host.h > @@ -811,6 +811,12 @@ struct kvm_vcpu_arch { > */ > struct kvm_mmu *walk_mmu; > > + /* > + * Protect cache from getting emptied in MMU shrinker while vCPU might > + * use cache for fault handling or loading MMU. As this is a per vCPU > + * lock, only contention might happen when MMU shrinker runs. > + */ > + struct mutex mmu_memory_cache_lock; > struct kvm_mmu_memory_cache mmu_pte_list_desc_cache; > struct kvm_mmu_memory_cache mmu_shadow_page_cache; > struct kvm_mmu_memory_cache mmu_shadowed_info_cache; > diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c > index 213e46b55dda..8e2935347615 100644 > --- a/arch/x86/kvm/mmu/mmu.c > +++ b/arch/x86/kvm/mmu/mmu.c > @@ -4524,29 +4524,33 @@ static int direct_page_fault(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault > if (r != RET_PF_INVALID) > return r; > > + mutex_lock(&vcpu->arch.mmu_memory_cache_lock); > r = mmu_topup_memory_caches(vcpu, false); > if (r) > - return r; > + goto out_mmu_memory_cache_unlock; > > r = kvm_faultin_pfn(vcpu, fault, ACC_ALL); > if (r != RET_PF_CONTINUE) > - return r; > + goto out_mmu_memory_cache_unlock; > > r = RET_PF_RETRY; > write_lock(&vcpu->kvm->mmu_lock); > > if (is_page_fault_stale(vcpu, fault)) > - goto out_unlock; > + goto out_mmu_unlock; > > r = make_mmu_pages_available(vcpu); > if (r) > - goto out_unlock; > + goto out_mmu_unlock; > > r = direct_map(vcpu, fault); > > -out_unlock: > +out_mmu_unlock: > write_unlock(&vcpu->kvm->mmu_lock); > kvm_release_pfn_clean(fault->pfn); > +out_mmu_memory_cache_unlock: > + mutex_unlock(&vcpu->arch.mmu_memory_cache_lock); > + > return r; > } > > @@ -4617,25 +4621,28 @@ static int kvm_tdp_mmu_page_fault(struct kvm_vcpu *vcpu, > if (r != RET_PF_INVALID) > return r; > > + mutex_lock(&vcpu->arch.mmu_memory_cache_lock); > r = mmu_topup_memory_caches(vcpu, false); > if (r) > - return r; > + goto out_mmu_memory_cache_unlock; > > r = kvm_faultin_pfn(vcpu, fault, ACC_ALL); > if (r != RET_PF_CONTINUE) > - return r; > + goto out_mmu_memory_cache_unlock; > > r = RET_PF_RETRY; > read_lock(&vcpu->kvm->mmu_lock); > > if (is_page_fault_stale(vcpu, fault)) > - goto out_unlock; > + goto out_mmu_unlock; > > r = kvm_tdp_mmu_map(vcpu, fault); > > -out_unlock: > +out_mmu_unlock: > read_unlock(&vcpu->kvm->mmu_lock); > kvm_release_pfn_clean(fault->pfn); > +out_mmu_memory_cache_unlock: > + mutex_unlock(&vcpu->arch.mmu_memory_cache_lock); > return r; > } > #endif > @@ -5691,6 +5698,7 @@ int kvm_mmu_load(struct kvm_vcpu *vcpu) > { > int r; > > + mutex_lock(&vcpu->arch.mmu_memory_cache_lock); > r = mmu_topup_memory_caches(vcpu, !vcpu->arch.mmu->root_role.direct); > if (r) > goto out; > @@ -5717,6 +5725,7 @@ int kvm_mmu_load(struct kvm_vcpu *vcpu) > */ > kvm_x86_call(flush_tlb_current)(vcpu); > out: > + mutex_unlock(&vcpu->arch.mmu_memory_cache_lock); > return r; > } > > @@ -6303,6 +6312,7 @@ int kvm_mmu_create(struct kvm_vcpu *vcpu) > if (!vcpu->arch.mmu_shadow_page_cache.init_value) > vcpu->arch.mmu_shadow_page_cache.gfp_zero = __GFP_ZERO; > > + mutex_init(&vcpu->arch.mmu_memory_cache_lock); > vcpu->arch.mmu = &vcpu->arch.root_mmu; > vcpu->arch.walk_mmu = &vcpu->arch.root_mmu; > > @@ -6997,13 +7007,50 @@ void kvm_mmu_invalidate_mmio_sptes(struct kvm *kvm, u64 gen) > static unsigned long mmu_shrink_scan(struct shrinker *shrink, > struct shrink_control *sc) > { > - return SHRINK_STOP; > + struct kvm *kvm, *next_kvm, *first_kvm = NULL; > + unsigned long i, freed = 0; > + struct kvm_vcpu *vcpu; > + > + mutex_lock(&kvm_lock); > + list_for_each_entry_safe(kvm, next_kvm, &vm_list, vm_list) { > + if (!first_kvm) > + first_kvm = kvm; > + else if (first_kvm == kvm) > + break; > + > + list_move_tail(&kvm->vm_list, &vm_list); > + > + kvm_for_each_vcpu(i, vcpu, kvm) { > + if (!mutex_trylock(&vcpu->arch.mmu_memory_cache_lock)) > + continue; > + freed += kvm_mmu_empty_memory_cache(&vcpu->arch.mmu_shadow_page_cache); > + freed += kvm_mmu_empty_memory_cache(&vcpu->arch.mmu_shadowed_info_cache); > + mutex_unlock(&vcpu->arch.mmu_memory_cache_lock); > + if (freed >= sc->nr_to_scan) > + goto out; Looking at the caller in mm/shrinker.c, sc->nr_to_scan will be <= 128 (SHRINK_BATCH), which is only enough for 2 vCPUs. So I think the shrinker will only ever free 2 vCPU caches of each VM (probably the first 2 vCPUs) before reordering the list and moving onto the next VM on the next call. Does that match the behavior you observe? > + } > + } > +out: > + mutex_unlock(&kvm_lock); > + return freed; > } > > static unsigned long mmu_shrink_count(struct shrinker *shrink, > struct shrink_control *sc) > { > - return SHRINK_EMPTY; > + unsigned long i, count = 0; > + struct kvm_vcpu *vcpu; > + struct kvm *kvm; > + > + mutex_lock(&kvm_lock); > + list_for_each_entry(kvm, &vm_list, vm_list) { > + kvm_for_each_vcpu(i, vcpu, kvm) { > + count += READ_ONCE(vcpu->arch.mmu_shadow_page_cache.nobjs); > + count += READ_ONCE(vcpu->arch.mmu_shadowed_info_cache.nobjs); > + } > + } > + mutex_unlock(&kvm_lock); > + return !count ? SHRINK_EMPTY : count; > } > > static struct shrinker *mmu_shrinker; > diff --git a/arch/x86/kvm/mmu/paging_tmpl.h b/arch/x86/kvm/mmu/paging_tmpl.h > index 405bd7ceee2a..084a5c532078 100644 > --- a/arch/x86/kvm/mmu/paging_tmpl.h > +++ b/arch/x86/kvm/mmu/paging_tmpl.h > @@ -809,13 +809,14 @@ static int FNAME(page_fault)(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault > return RET_PF_EMULATE; > } > > + mutex_lock(&vcpu->arch.mmu_memory_cache_lock); > r = mmu_topup_memory_caches(vcpu, true); > if (r) > - return r; > + goto out_mmu_memory_cache_unlock; > > r = kvm_faultin_pfn(vcpu, fault, walker.pte_access); > if (r != RET_PF_CONTINUE) > - return r; > + goto out_mmu_memory_cache_unlock; > > /* > * Do not change pte_access if the pfn is a mmio page, otherwise > @@ -840,16 +841,19 @@ static int FNAME(page_fault)(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault > write_lock(&vcpu->kvm->mmu_lock); > > if (is_page_fault_stale(vcpu, fault)) > - goto out_unlock; > + goto out_mmu_unlock; > > r = make_mmu_pages_available(vcpu); > if (r) > - goto out_unlock; > + goto out_mmu_unlock; > r = FNAME(fetch)(vcpu, fault, &walker); > > -out_unlock: > +out_mmu_unlock: > write_unlock(&vcpu->kvm->mmu_lock); > kvm_release_pfn_clean(fault->pfn); > +out_mmu_memory_cache_unlock: > + mutex_unlock(&vcpu->arch.mmu_memory_cache_lock); > + > return r; > } > > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h > index b23c6d48392f..288e503f14a0 100644 > --- a/include/linux/kvm_host.h > +++ b/include/linux/kvm_host.h > @@ -1446,6 +1446,7 @@ void kvm_flush_remote_tlbs_memslot(struct kvm *kvm, > int kvm_mmu_topup_memory_cache(struct kvm_mmu_memory_cache *mc, int min); > int __kvm_mmu_topup_memory_cache(struct kvm_mmu_memory_cache *mc, int capacity, int min); > int kvm_mmu_memory_cache_nr_free_objects(struct kvm_mmu_memory_cache *mc); > +int kvm_mmu_empty_memory_cache(struct kvm_mmu_memory_cache *mc); > void kvm_mmu_free_memory_cache(struct kvm_mmu_memory_cache *mc); > void *kvm_mmu_memory_cache_alloc(struct kvm_mmu_memory_cache *mc); > #endif > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c > index cb2b78e92910..5d89ca218791 100644 > --- a/virt/kvm/kvm_main.c > +++ b/virt/kvm/kvm_main.c > @@ -451,15 +451,21 @@ int kvm_mmu_memory_cache_nr_free_objects(struct kvm_mmu_memory_cache *mc) > return mc->nobjs; > } > > -void kvm_mmu_free_memory_cache(struct kvm_mmu_memory_cache *mc) > +int kvm_mmu_empty_memory_cache(struct kvm_mmu_memory_cache *mc) > { > + int freed = mc->nobjs; > while (mc->nobjs) { > if (mc->kmem_cache) > kmem_cache_free(mc->kmem_cache, mc->objects[--mc->nobjs]); > else > free_page((unsigned long)mc->objects[--mc->nobjs]); > } > + return freed; > +} > > +void kvm_mmu_free_memory_cache(struct kvm_mmu_memory_cache *mc) > +{ > + kvm_mmu_empty_memory_cache(mc); > kvfree(mc->objects); > > mc->objects = NULL; > -- > 2.46.0.662.g92d0881bb0-goog >