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Wed, 14 Jan 2026 13:55:52 +0000 (UTC) X-Farcaster-Flow-ID: 8a859852-980a-4ccf-94d2-9c29b54debef Received: from EX19D005EUB003.ant.amazon.com (10.252.51.31) by EX19MTAEUA001.ant.amazon.com (10.252.50.50) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA) id 15.2.2562.35; Wed, 14 Jan 2026 13:55:51 +0000 Received: from [192.168.15.25] (10.106.82.12) by EX19D005EUB003.ant.amazon.com (10.252.51.31) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA) id 15.2.2562.35; Wed, 14 Jan 2026 13:55:48 +0000 Message-ID: Date: Wed, 14 Jan 2026 13:55:43 +0000 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Reply-To: Subject: Re: [PATCH v8 05/13] KVM: guest_memfd: Add flag to remove from direct map To: Vlastimil Babka , "Kalyazin, Nikita" , "kvm@vger.kernel.org" , "linux-doc@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "kvmarm@lists.linux.dev" , "linux-fsdevel@vger.kernel.org" , "linux-mm@kvack.org" , "bpf@vger.kernel.org" , "linux-kselftest@vger.kernel.org" CC: "pbonzini@redhat.com" , "corbet@lwn.net" , "maz@kernel.org" , "oupton@kernel.org" , "joey.gouly@arm.com" , "suzuki.poulose@arm.com" , "yuzenghui@huawei.com" , "catalin.marinas@arm.com" , "will@kernel.org" , "seanjc@google.com" , "tglx@linutronix.de" , "mingo@redhat.com" , "bp@alien8.de" , "dave.hansen@linux.intel.com" , "x86@kernel.org" , "hpa@zytor.com" , "luto@kernel.org" , "peterz@infradead.org" , "willy@infradead.org" , "akpm@linux-foundation.org" , "david@kernel.org" , "lorenzo.stoakes@oracle.com" , "Liam.Howlett@oracle.com" , "rppt@kernel.org" , "surenb@google.com" , "mhocko@suse.com" , "ast@kernel.org" , "daniel@iogearbox.net" , "andrii@kernel.org" , "martin.lau@linux.dev" , "eddyz87@gmail.com" , "song@kernel.org" , "yonghong.song@linux.dev" , "john.fastabend@gmail.com" , "kpsingh@kernel.org" , "sdf@fomichev.me" , "haoluo@google.com" , "jolsa@kernel.org" , "jgg@ziepe.ca" , "jhubbard@nvidia.com" , "peterx@redhat.com" , "jannh@google.com" , "pfalcato@suse.de" , "shuah@kernel.org" , "riel@surriel.com" , "baohua@kernel.org" , "ryan.roberts@arm.com" , "jgross@suse.com" , "yu-cheng.yu@intel.com" , "kas@kernel.org" , "coxu@redhat.com" , "kevin.brodsky@arm.com" , "ackerleytng@google.com" , "maobibo@loongson.cn" , "prsampat@amd.com" , "mlevitsk@redhat.com" , "isaku.yamahata@intel.com" , "jmattson@google.com" , "jthoughton@google.com" , "linux-arm-kernel@lists.infradead.org" , "vannapurve@google.com" , "jackmanb@google.com" , "aneesh.kumar@kernel.org" , "patrick.roy@linux.dev" , "Thomson, Jack" , "Itazuri, Takahiro" , "Manwaring, Derek" , "Cali, Marco" References: <20251205165743.9341-1-kalyazin@amazon.com> <20251205165743.9341-6-kalyazin@amazon.com> Content-Language: en-US From: Nikita Kalyazin Autocrypt: addr=kalyazin@amazon.com; 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>> + unsigned long addr = (unsigned long) folio_address(folio); >> + u64 gmem_flags = GMEM_I(folio_inode(folio))->flags; >> + >> + if (kvm_gmem_folio_no_direct_map(folio) || !(gmem_flags & GUEST_MEMFD_FLAG_NO_DIRECT_MAP)) >> + goto out; >> + >> + r = set_direct_map_valid_noflush(folio_page(folio, 0), folio_nr_pages(folio), >> + false); >> + >> + if (r) >> + goto out; >> + >> + folio->private = (void *) KVM_GMEM_FOLIO_NO_DIRECT_MAP; > > With Dave's suggestion on patch 1/13 to have folio_zap_direct_map(), setting > this folio->private flag wouldn't be possible between the zap and tlb flush, > but it's not an issue to set it before the zap, right? I can't see an issue with that. Did it in the v9. > >> + flush_tlb_kernel_range(addr, addr + folio_size(folio)); >> + >> +out: >> + return r; >> +} >> + >> +static void kvm_gmem_folio_restore_direct_map(struct folio *folio) >> +{ >> + /* >> + * Direct map restoration cannot fail, as the only error condition >> + * for direct map manipulation is failure to allocate page tables >> + * when splitting huge pages, but this split would have already >> + * happened in set_direct_map_invalid_noflush() in kvm_gmem_folio_zap_direct_map(). >> + * Thus set_direct_map_valid_noflush() here only updates prot bits. >> + */ >> + if (kvm_gmem_folio_no_direct_map(folio)) >> + set_direct_map_valid_noflush(folio_page(folio, 0), folio_nr_pages(folio), >> + true); > > I think you're missing here clearing KVM_GMEM_FOLIO_NO_DIRECT_MAP from > folio->private, which means if there's another > kvm_gmem_folio_zap_direct_map() call on it in the future, it will do nothing? You're very right, thanks. Fixed in the v9. > >> +} >> + >> static inline void kvm_gmem_mark_prepared(struct folio *folio) >> { >> folio_mark_uptodate(folio); >> @@ -398,6 +444,7 @@ static vm_fault_t kvm_gmem_fault_user_mapping(struct vm_fault *vmf) >> struct inode *inode = file_inode(vmf->vma->vm_file); >> struct folio *folio; >> vm_fault_t ret = VM_FAULT_LOCKED; >> + int err; >> >> if (((loff_t)vmf->pgoff << PAGE_SHIFT) >= i_size_read(inode)) >> return VM_FAULT_SIGBUS; >> @@ -423,6 +470,12 @@ static vm_fault_t kvm_gmem_fault_user_mapping(struct vm_fault *vmf) >> kvm_gmem_mark_prepared(folio); >> } >> >> + err = kvm_gmem_folio_zap_direct_map(folio); >> + if (err) { >> + ret = vmf_error(err); >> + goto out_folio; >> + } >> + >> vmf->page = folio_file_page(folio, vmf->pgoff); >> >> out_folio: >> @@ -533,6 +586,8 @@ static void kvm_gmem_free_folio(struct folio *folio) >> kvm_pfn_t pfn = page_to_pfn(page); >> int order = folio_order(folio); >> >> + kvm_gmem_folio_restore_direct_map(folio); >> + >> kvm_arch_gmem_invalidate(pfn, pfn + (1ul << order)); >> } >> >> @@ -596,6 +651,9 @@ static int __kvm_gmem_create(struct kvm *kvm, loff_t size, u64 flags) >> /* Unmovable mappings are supposed to be marked unevictable as well. */ >> WARN_ON_ONCE(!mapping_unevictable(inode->i_mapping)); >> >> + if (flags & GUEST_MEMFD_FLAG_NO_DIRECT_MAP) >> + mapping_set_no_direct_map(inode->i_mapping); >> + >> GMEM_I(inode)->flags = flags; >> >> file = alloc_file_pseudo(inode, kvm_gmem_mnt, name, O_RDWR, &kvm_gmem_fops); >> @@ -807,6 +865,8 @@ int kvm_gmem_get_pfn(struct kvm *kvm, struct kvm_memory_slot *slot, >> if (!is_prepared) >> r = kvm_gmem_prepare_folio(kvm, slot, gfn, folio); >> >> + kvm_gmem_folio_zap_direct_map(folio); >> + >> folio_unlock(folio); >> >> if (!r) >