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[95.172.185.203]) by smtp.gmail.com with ESMTPSA id t1-20020a05600c41c100b003dc47d458cdsm81138wmh.15.2023.01.27.13.36.54 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 27 Jan 2023 13:36:55 -0800 (PST) Date: Fri, 27 Jan 2023 23:36:52 +0200 From: Zhi Wang To: Sean Christopherson Cc: isaku.yamahata@intel.com, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, isaku.yamahata@gmail.com, Paolo Bonzini , erdemaktas@google.com, Sagi Shahar , David Matlack , Sean Christopherson , kai.huang@intel.com Subject: Re: [PATCH v11 030/113] KVM: x86/mmu: Replace hardcoded value 0 for the initial value for SPTE Message-ID: <20230127233513.0000367c@gmail.com> In-Reply-To: References: <20230125112434.0000512a@gmail.com> X-Mailer: Claws Mail 4.1.0 (GTK 3.24.33; x86_64-w64-mingw32) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 25 Jan 2023 17:22:08 +0000 Sean Christopherson wrote: > On Wed, Jan 25, 2023, Zhi Wang wrote: > > On Thu, 12 Jan 2023 08:31:38 -0800 > > isaku.yamahata@intel.com wrote: > > > > This refactor patch is quite hacky. > > > > Why not change the purpose of vcpu->arch.mmu_shadow_page.gfp_zero and let the > > callers respect that the initial value of spte can be configurable? It will be > > generic and not TDX-specific, then kvm_init_shadow_page() is not required, > > mmu_topup_shadow_page_cache() can be left un-touched as the refactor can cover > > other architectures. > > > > 1) Let it store the expected nonpresent value and rename it to nonpresent_spte. > > > I agree that handling this in the common code would be cleaner, but repurposing > gfp_zero gets kludgy because it would require a magic value to say "don't initialize > the data", e.g. x86's mmu_shadowed_info_cache isn't pre-filled. > > And supporting a custom 64-bit init value for kmem_cache-backed caches would require > restricting such caches to be a multiple of 8 bytes in size. > > How about this? Lightly tested. > > From: Sean Christopherson > Date: Wed, 25 Jan 2023 16:55:01 +0000 > Subject: [PATCH] KVM: Allow page-sized MMU caches to be initialized with > custom 64-bit values > It looks good enough so far although it only supports 64bit init value. But it can be extended in the future. Just want to make sure people are thinking the same: 1) Keep the changes of SHADOW_NONPRESENT_VALUE and REMOVED_SPTE in TDX patch. init_value stays as a generic feature in the kvm mmu cache layer. It is *not* going to replace SHADOW_NONPRESENT_VALUE. 2) TDX kvm_x86_vcpu_create sets the SHADOW_NONPRESENT value into init_value. 3) mmu cache topping up function initializes the page according to init_value with Sean's patch. > Add support to MMU caches for initializing a page with a custom 64-bit > value, e.g. to pre-fill an entire page table with non-zero PTE values. > The functionality will be used by x86 to support Intel's TDX, which needs > to set bit 63 in all non-present PTEs in order to prevent !PRESENT page > faults from getting reflected into the guest (Intel's EPT Violation #VE > architecture made the less than brilliant decision of having the per-PTE > behavior be opt-out instead of opt-in). > > Signed-off-by: Sean Christopherson > --- > include/linux/kvm_types.h | 1 + > virt/kvm/kvm_main.c | 16 ++++++++++++++-- > 2 files changed, 15 insertions(+), 2 deletions(-) > > diff --git a/include/linux/kvm_types.h b/include/linux/kvm_types.h > index 76de36e56cdf..67972db17b55 100644 > --- a/include/linux/kvm_types.h > +++ b/include/linux/kvm_types.h > @@ -94,6 +94,7 @@ struct kvm_mmu_memory_cache { > int nobjs; > gfp_t gfp_zero; > gfp_t gfp_custom; > + u64 init_value; > struct kmem_cache *kmem_cache; > int capacity; > void **objects; > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c > index d255964ec331..78f1e49179a7 100644 > --- a/virt/kvm/kvm_main.c > +++ b/virt/kvm/kvm_main.c > @@ -380,12 +380,17 @@ static void kvm_flush_shadow_all(struct kvm *kvm) > static inline void *mmu_memory_cache_alloc_obj(struct kvm_mmu_memory_cache *mc, > gfp_t gfp_flags) > { > + void *page; > + > gfp_flags |= mc->gfp_zero; > > if (mc->kmem_cache) > return kmem_cache_alloc(mc->kmem_cache, gfp_flags); > - else > - return (void *)__get_free_page(gfp_flags); > + > + page = (void *)__get_free_page(gfp_flags); > + if (page && mc->init_value) > + memset64(page, mc->init_value, PAGE_SIZE / sizeof(mc->init_value)); > + return page; > } > > int __kvm_mmu_topup_memory_cache(struct kvm_mmu_memory_cache *mc, int capacity, int min) > @@ -400,6 +405,13 @@ int __kvm_mmu_topup_memory_cache(struct kvm_mmu_memory_cache *mc, int capacity, > if (WARN_ON_ONCE(!capacity)) > return -EIO; > > + /* > + * Custom init values can be used only for page allocations, > + * and obviously conflict with __GFP_ZERO. > + */ > + if (WARN_ON_ONCE(mc->init_value && (mc->kmem_cache || mc->gfp_zero))) > + return -EIO; > + > mc->objects = kvmalloc_array(sizeof(void *), capacity, gfp); > if (!mc->objects) > return -ENOMEM; > > base-commit: 503f0315c97739d3f8e645c500d81757dfbf76be