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Tue, 07 May 2024 10:48:18 -0700 (PDT) Received: from [192.168.10.81] ([151.95.155.52]) by smtp.googlemail.com with ESMTPSA id b14-20020a0564021f0e00b00572cebc5f32sm5776641edb.65.2024.05.07.10.48.16 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 07 May 2024 10:48:17 -0700 (PDT) Message-ID: <044e8953-56f0-405e-9b50-7dde4ca8986b@redhat.com> Date: Tue, 7 May 2024 19:48:15 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v15 02/20] KVM: x86: Add hook for determining max NPT mapping level To: Michael Roth , kvm@vger.kernel.org Cc: linux-coco@lists.linux.dev, linux-mm@kvack.org, linux-crypto@vger.kernel.org, x86@kernel.org, linux-kernel@vger.kernel.org, tglx@linutronix.de, mingo@redhat.com, jroedel@suse.de, thomas.lendacky@amd.com, hpa@zytor.com, ardb@kernel.org, seanjc@google.com, vkuznets@redhat.com, jmattson@google.com, luto@kernel.org, dave.hansen@linux.intel.com, slp@redhat.com, pgonda@google.com, peterz@infradead.org, srinivas.pandruvada@linux.intel.com, rientjes@google.com, dovmurik@linux.ibm.com, tobin@ibm.com, bp@alien8.de, vbabka@suse.cz, kirill@shutemov.name, ak@linux.intel.com, tony.luck@intel.com, sathyanarayanan.kuppuswamy@linux.intel.com, alpergun@google.com, jarkko@kernel.org, ashish.kalra@amd.com, nikunj.dadhania@amd.com, pankaj.gupta@amd.com, liam.merwick@oracle.com References: <20240501085210.2213060-1-michael.roth@amd.com> <20240501085210.2213060-3-michael.roth@amd.com> From: Paolo Bonzini Autocrypt: addr=pbonzini@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 406C5160013 X-Stat-Signature: cumywiekum3yjwjhx8g3tcp7erpp6wh5 X-HE-Tag: 1715104102-977546 X-HE-Meta: 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 4/d2ZAkK 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 5/1/24 10:51, Michael Roth wrote: > In the case of SEV-SNP, whether or not a 2MB page can be mapped via a > 2MB mapping in the guest's nested page table depends on whether or not > any subpages within the range have already been initialized as private > in the RMP table. The existing mixed-attribute tracking in KVM is > insufficient here, for instance: > > - gmem allocates 2MB page > - guest issues PVALIDATE on 2MB page > - guest later converts a subpage to shared > - SNP host code issues PSMASH to split 2MB RMP mapping to 4K > - KVM MMU splits NPT mapping to 4K > - guest later converts that shared page back to private > > At this point there are no mixed attributes, and KVM would normally > allow for 2MB NPT mappings again, but this is actually not allowed > because the RMP table mappings are 4K and cannot be promoted on the > hypervisor side, so the NPT mappings must still be limited to 4K to > match this. > > Add a hook to determine the max NPT mapping size in situations like > this. > > Suggested-by: Sean Christopherson > Signed-off-by: Michael Roth > --- > arch/x86/include/asm/kvm-x86-ops.h | 1 + > arch/x86/include/asm/kvm_host.h | 1 + > arch/x86/kvm/mmu/mmu.c | 18 ++++++++++++++++-- > 3 files changed, 18 insertions(+), 2 deletions(-) > > diff --git a/arch/x86/include/asm/kvm-x86-ops.h b/arch/x86/include/asm/kvm-x86-ops.h > index c81990937ab4..566d19b02483 100644 > --- a/arch/x86/include/asm/kvm-x86-ops.h > +++ b/arch/x86/include/asm/kvm-x86-ops.h > @@ -140,6 +140,7 @@ KVM_X86_OP_OPTIONAL_RET0(vcpu_get_apicv_inhibit_reasons); > KVM_X86_OP_OPTIONAL(get_untagged_addr) > KVM_X86_OP_OPTIONAL(alloc_apic_backing_page) > KVM_X86_OP_OPTIONAL_RET0(gmem_prepare) > +KVM_X86_OP_OPTIONAL_RET0(private_max_mapping_level) > KVM_X86_OP_OPTIONAL(gmem_invalidate) > > #undef KVM_X86_OP > diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h > index c6c5018376be..87265b73906a 100644 > --- a/arch/x86/include/asm/kvm_host.h > +++ b/arch/x86/include/asm/kvm_host.h > @@ -1816,6 +1816,7 @@ struct kvm_x86_ops { > void *(*alloc_apic_backing_page)(struct kvm_vcpu *vcpu); > int (*gmem_prepare)(struct kvm *kvm, kvm_pfn_t pfn, gfn_t gfn, int max_order); > void (*gmem_invalidate)(kvm_pfn_t start, kvm_pfn_t end); > + int (*private_max_mapping_level)(struct kvm *kvm, kvm_pfn_t pfn); > }; > > struct kvm_x86_nested_ops { > diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c > index 510eb1117012..0d556da052f6 100644 > --- a/arch/x86/kvm/mmu/mmu.c > +++ b/arch/x86/kvm/mmu/mmu.c > @@ -4271,6 +4271,20 @@ static inline u8 kvm_max_level_for_order(int order) > return PG_LEVEL_4K; > } > > +static u8 kvm_max_private_mapping_level(struct kvm *kvm, kvm_pfn_t pfn, > + u8 max_level, int gmem_order) > +{ > + if (max_level == PG_LEVEL_4K) > + return PG_LEVEL_4K; > + > + max_level = min(kvm_max_level_for_order(gmem_order), max_level); > + if (max_level == PG_LEVEL_4K) > + return PG_LEVEL_4K; > + > + return min(max_level, > + static_call(kvm_x86_private_max_mapping_level)(kvm, pfn)); > +} Since you're returning 0 both as a default and, later in the series, for non-SNP guests, you need to treat 0 as "don't care": diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c index de35dee25bf6..62ad38b2a8c9 100644 --- a/arch/x86/kvm/mmu/mmu.c +++ b/arch/x86/kvm/mmu/mmu.c @@ -4274,6 +4274,8 @@ static inline u8 kvm_max_level_for_order(int order) static u8 kvm_max_private_mapping_level(struct kvm *kvm, kvm_pfn_t pfn, u8 max_level, int gmem_order) { + u8 req_max_level; + if (max_level == PG_LEVEL_4K) return PG_LEVEL_4K; @@ -4281,8 +4283,11 @@ static u8 kvm_max_private_mapping_level(struct kvm *kvm, kvm_pfn_t pfn, if (max_level == PG_LEVEL_4K) return PG_LEVEL_4K; - return min(max_level, - static_call(kvm_x86_private_max_mapping_level)(kvm, pfn)); + req_max_level = static_call(kvm_x86_private_max_mapping_level)(kvm, pfn); + if (req_max_level) + max_level = min(max_level, req_max_level); + + return req_max_level; } static int kvm_faultin_pfn_private(struct kvm_vcpu *vcpu, Not beautiful but it does the job I guess. Paolo