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[2003:d8:2f25:9c00:e2c7:6eb5:8a51:1c60]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-3a35ca5a84csm19693528f8f.31.2025.05.21.05.44.27 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 21 May 2025 05:44:29 -0700 (PDT) Message-ID: Date: Wed, 21 May 2025 14:44:26 +0200 Precedence: bulk X-Mailing-List: linux-arm-msm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v9 14/17] KVM: arm64: Enable mapping guest_memfd in arm64 To: Fuad Tabba Cc: kvm@vger.kernel.org, linux-arm-msm@vger.kernel.org, linux-mm@kvack.org, 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, xiaoyao.li@intel.com, 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, 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: <20250513163438.3942405-1-tabba@google.com> <20250513163438.3942405-15-tabba@google.com> <2084504e-2a11-404a-bbe8-930384106f53@redhat.com> From: David Hildenbrand Content-Language: en-US Autocrypt: addr=david@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 21.05.25 12:29, Fuad Tabba wrote: > On Wed, 21 May 2025 at 11:26, David Hildenbrand wrote: >> >> On 21.05.25 12:12, Fuad Tabba wrote: >>> Hi David, >>> >>> On Wed, 21 May 2025 at 09:05, David Hildenbrand wrote: >>>> >>>> On 13.05.25 18:34, Fuad Tabba wrote: >>>>> Enable mapping guest_memfd in arm64. For now, it applies to all >>>>> VMs in arm64 that use guest_memfd. In the future, new VM types >>>>> can restrict this via kvm_arch_gmem_supports_shared_mem(). >>>>> >>>>> Signed-off-by: Fuad Tabba >>>>> --- >>>>> arch/arm64/include/asm/kvm_host.h | 10 ++++++++++ >>>>> arch/arm64/kvm/Kconfig | 1 + >>>>> 2 files changed, 11 insertions(+) >>>>> >>>>> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h >>>>> index 08ba91e6fb03..2514779f5131 100644 >>>>> --- a/arch/arm64/include/asm/kvm_host.h >>>>> +++ b/arch/arm64/include/asm/kvm_host.h >>>>> @@ -1593,4 +1593,14 @@ static inline bool kvm_arch_has_irq_bypass(void) >>>>> return true; >>>>> } >>>>> >>>>> +static inline bool kvm_arch_supports_gmem(struct kvm *kvm) >>>>> +{ >>>>> + return IS_ENABLED(CONFIG_KVM_GMEM); >>>>> +} >>>>> + >>>>> +static inline bool kvm_arch_vm_supports_gmem_shared_mem(struct kvm *kvm) >>>>> +{ >>>>> + return IS_ENABLED(CONFIG_KVM_GMEM_SHARED_MEM); >>>>> +} >>>>> + >>>>> #endif /* __ARM64_KVM_HOST_H__ */ >>>>> diff --git a/arch/arm64/kvm/Kconfig b/arch/arm64/kvm/Kconfig >>>>> index 096e45acadb2..8c1e1964b46a 100644 >>>>> --- a/arch/arm64/kvm/Kconfig >>>>> +++ b/arch/arm64/kvm/Kconfig >>>>> @@ -38,6 +38,7 @@ menuconfig KVM >>>>> select HAVE_KVM_VCPU_RUN_PID_CHANGE >>>>> select SCHED_INFO >>>>> select GUEST_PERF_EVENTS if PERF_EVENTS >>>>> + select KVM_GMEM_SHARED_MEM >>>>> help >>>>> Support hosting virtualized guest machines. >>>>> >>>> >>>> Do we have to reject somewhere if we are given a guest_memfd that was >>>> *not* created using the SHARED flag? Or will existing checks already >>>> reject that? >>> >>> We don't reject, but I don't think we need to. A user can create a >>> guest_memfd that's private in arm64, it would just be useless. >> >> But the arm64 fault routine would not be able to handle that properly, no? > > Actually it would. The function user_mem_abort() doesn't care whether > it's private or shared. It would fault it into the guest correctly > regardless. I think what I meant is that: if it's !shared (private only), shared accesses (IOW all access without CoCo) should be taken from the user space mapping. But user_mem_abort() would blindly go to kvm_gmem_get_pfn() because "is_gmem = kvm_slot_has_gmem(memslot) = true". In other words, arm64 would have to *ignore* guest_memfd that does not support shared? That's why I was wondering whether we should just immediately refuse such guest_memfds. -- Cheers, David / dhildenb