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X-CSE-ConnectionGUID: OJp3gODqTKuf04LMdByTug== X-CSE-MsgGUID: NBDxx5mZSiC1FYdiECZTzA== X-IronPort-AV: E=McAfee;i="6800,10657,11495"; a="55228314" X-IronPort-AV: E=Sophos;i="6.16,320,1744095600"; d="scan'208";a="55228314" Received: from fmviesa010.fm.intel.com ([10.60.135.150]) by orvoesa110.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 17 Jul 2025 22:10:21 -0700 X-CSE-ConnectionGUID: a9b4WvSRTtaaMhuxuVj91Q== X-CSE-MsgGUID: TqPVZm1bRiiCBhRpewpQBA== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.16,320,1744095600"; d="scan'208";a="158671869" Received: from xiaoyaol-hp-g830.ccr.corp.intel.com (HELO [10.124.247.1]) ([10.124.247.1]) by fmviesa010-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 17 Jul 2025 22:10:04 -0700 Message-ID: <8340ec70-1c44-47a7-8c48-89e175501e89@intel.com> Date: Fri, 18 Jul 2025 13:10:00 +0800 Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v15 11/21] KVM: x86/mmu: Allow NULL-able fault in kvm_max_private_mapping_level To: Fuad Tabba , kvm@vger.kernel.org, linux-arm-msm@vger.kernel.org, linux-mm@kvack.org, kvmarm@lists.linux.dev Cc: pbonzini@redhat.com, chenhuacai@kernel.org, mpe@ellerman.id.au, anup@brainfault.org, paul.walmsley@sifive.com, palmer@dabbelt.com, aou@eecs.berkeley.edu, seanjc@google.com, viro@zeniv.linux.org.uk, brauner@kernel.org, willy@infradead.org, akpm@linux-foundation.org, yilun.xu@intel.com, chao.p.peng@linux.intel.com, jarkko@kernel.org, amoorthy@google.com, dmatlack@google.com, isaku.yamahata@intel.com, mic@digikod.net, vbabka@suse.cz, vannapurve@google.com, ackerleytng@google.com, mail@maciej.szmigiero.name, david@redhat.com, michael.roth@amd.com, wei.w.wang@intel.com, liam.merwick@oracle.com, isaku.yamahata@gmail.com, kirill.shutemov@linux.intel.com, suzuki.poulose@arm.com, steven.price@arm.com, quic_eberman@quicinc.com, quic_mnalajal@quicinc.com, quic_tsoni@quicinc.com, quic_svaddagi@quicinc.com, quic_cvanscha@quicinc.com, quic_pderrin@quicinc.com, quic_pheragu@quicinc.com, catalin.marinas@arm.com, james.morse@arm.com, yuzenghui@huawei.com, oliver.upton@linux.dev, maz@kernel.org, will@kernel.org, qperret@google.com, keirf@google.com, roypat@amazon.co.uk, shuah@kernel.org, hch@infradead.org, jgg@nvidia.com, rientjes@google.com, jhubbard@nvidia.com, fvdl@google.com, hughd@google.com, jthoughton@google.com, peterx@redhat.com, pankaj.gupta@amd.com, ira.weiny@intel.com References: <20250717162731.446579-1-tabba@google.com> <20250717162731.446579-12-tabba@google.com> Content-Language: en-US From: Xiaoyao Li In-Reply-To: <20250717162731.446579-12-tabba@google.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 7/18/2025 12:27 AM, Fuad Tabba wrote: > From: Ackerley Tng > > Refactor kvm_max_private_mapping_level() to accept a NULL kvm_page_fault > pointer and rename it to kvm_gmem_max_mapping_level(). > > The max_mapping_level x86 operation (previously private_max_mapping_level) > is designed to potentially be called without an active page fault, for > instance, when kvm_mmu_max_mapping_level() is determining the maximum > mapping level for a gfn proactively. > > Allow NULL fault pointer: Modify kvm_max_private_mapping_level() to > safely handle a NULL fault argument. This aligns its interface with the > kvm_x86_ops.max_mapping_level operation it wraps, which can also be > called with NULL. are you sure of it? The patch 09 just added the check of fault->is_private for TDX and SEV. > Rename function to kvm_gmem_max_mapping_level(): This reinforces that > the function's scope is for guest_memfd-backed memory, which can be > either private or non-private, removing any remaining "private" > connotation from its name. > > Optimize max_level checks: Introduce a check in the caller to skip > querying for max_mapping_level if the current max_level is already > PG_LEVEL_4K, as no further reduction is possible. > > Acked-by: David Hildenbrand > Suggested-by: Sean Christoperson > Signed-off-by: Ackerley Tng > Signed-off-by: Fuad Tabba > --- > arch/x86/kvm/mmu/mmu.c | 16 +++++++--------- > 1 file changed, 7 insertions(+), 9 deletions(-) > > diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c > index bb925994cbc5..6bd28fda0fd3 100644 > --- a/arch/x86/kvm/mmu/mmu.c > +++ b/arch/x86/kvm/mmu/mmu.c > @@ -4467,17 +4467,13 @@ static inline u8 kvm_max_level_for_order(int order) > return PG_LEVEL_4K; > } > > -static u8 kvm_max_private_mapping_level(struct kvm *kvm, > - struct kvm_page_fault *fault, > - int gmem_order) > +static u8 kvm_gmem_max_mapping_level(struct kvm *kvm, int order, > + struct kvm_page_fault *fault) > { > - u8 max_level = fault->max_level; > u8 req_max_level; > + u8 max_level; > > - if (max_level == PG_LEVEL_4K) > - return PG_LEVEL_4K; > - > - max_level = min(kvm_max_level_for_order(gmem_order), max_level); > + max_level = kvm_max_level_for_order(order); > if (max_level == PG_LEVEL_4K) > return PG_LEVEL_4K; > > @@ -4513,7 +4509,9 @@ static int kvm_mmu_faultin_pfn_private(struct kvm_vcpu *vcpu, > } > > fault->map_writable = !(fault->slot->flags & KVM_MEM_READONLY); > - fault->max_level = kvm_max_private_mapping_level(vcpu->kvm, fault, max_order); > + if (fault->max_level >= PG_LEVEL_4K) > + fault->max_level = kvm_gmem_max_mapping_level(vcpu->kvm, > + max_order, fault); I cannot understand why this change is required. In what case will fault->max_level < PG_LEVEL_4K? > return RET_PF_CONTINUE; > }