From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 52CE531BC8F for ; Thu, 25 Sep 2025 19:28:54 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=170.10.129.124 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1758828536; cv=none; b=C9MAz3Q9O0PLmDGyptaG4k/0u0Te+2kqsLqBKqV0HV4J4jchItTm+dPhYxEABMoK6ytSgYqUBUKpIZWD8bV1zsQMBb6JgomxS3qUiJTnMCF7yYVcUex4+JNodyld17cK2KUYezKx0JR8N2VGxbfa0DbqyXNtt8/X3yIbgyOu6o4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1758828536; c=relaxed/simple; bh=kOCORXCAXXJ2qj0YE5bKRj+HTBCxeKD9S0E68rhLDkk=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=LdPiO6vfau7uI5hKrqGOefnWISioIVzaJS1ByCRDvdO1OXcD9Biv/JmoRzWDtKrjCt7PbNe6hx18YU20xJoO3ffI2mPPs+aiB60+VhLtcJRVC8lBvwUtPoeGp4RE+tYtsZ3lDo9zwotPAyCBZ6an6d5brmUbWyxUuUkmg0xP1cE= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com; spf=pass smtp.mailfrom=redhat.com; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b=AV1u3umb; arc=none smtp.client-ip=170.10.129.124 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=quarantine dis=none) header.from=redhat.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=redhat.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="AV1u3umb" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1758828533; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:autocrypt:autocrypt; bh=Bq7ppmqVgZHliLbZBRvvT4qAn03nm4JKVOlNO1X6M5U=; b=AV1u3umb3hAJ0jcLxmdhLYawnY0G3iX1qbhr/VYpjd2MkS1bb516uC2cZCceG9a3Dfz0QQ 0L1P/WseG94jvUw92qeeP6wreJBTJL0QdHJSQ+NjosQXZkOorpwMjSWXdWELAX7B5Ab/Sk Dz33CVrxT32WL8X1SGZiyFj1Olb8N7s= Received: from mail-wm1-f69.google.com (mail-wm1-f69.google.com [209.85.128.69]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-113-cBnBcFQiMryVx8vBMrGy0w-1; Thu, 25 Sep 2025 15:28:52 -0400 X-MC-Unique: cBnBcFQiMryVx8vBMrGy0w-1 X-Mimecast-MFC-AGG-ID: cBnBcFQiMryVx8vBMrGy0w_1758828531 Received: by mail-wm1-f69.google.com with SMTP id 5b1f17b1804b1-45df7e734e0so7057355e9.0 for ; Thu, 25 Sep 2025 12:28:51 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1758828531; x=1759433331; h=content-transfer-encoding:in-reply-to:autocrypt:content-language :from:references:cc:to:subject:user-agent:mime-version:date :message-id:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=Bq7ppmqVgZHliLbZBRvvT4qAn03nm4JKVOlNO1X6M5U=; b=E16/N5brTRHgOsMD5qswVD50b2HkZtiLi7piLVuPOeGH3ego6JFN/K6F1afaKeOgyl dDHGAPT1zRFakb4YyJN9xVL3n8aY62+b5euXuMJV9bk0MxBNKBrshClwE5pKuKBgKss2 Q8iFt2ATr/iSAKbV/sjnmAJes9vJ035caVQupnhR2fLySytOQTB4Bpl9vYmLMrSTi2df bQ5sI/2i9iKVy43GdfTeMJJDJ0V9TPMGRBzyZj1giMsSzl0jshHxIdINRYiLJXYiWGk2 HO8NStiRBMAVt/QjSJXmkVmoosMN4w+BexKV6d6ClPpdVJP0bHSsGlF2JyLVDmaksj5V 8ZLw== X-Forwarded-Encrypted: i=1; AJvYcCV64ZM0esxECiM02wIhRScPeNUJpwXr87f6lLRnO8nzfXU5lFcELq7OoKsLRPlXYaH1gDwcL8rDa0N4Zt0=@vger.kernel.org X-Gm-Message-State: AOJu0YwAoGAtDKZBMDoAqAFtWhUpuOHFcJKgDizFxRuazMD7uDxdaeCf gsbKf68qAd11fDqIUvLz2RcEo8DbC6KCtwm+5VE/eMWMrE8IbmoMTuqkPxdQ9dG0XO+H00pqUHb pKiny+bopqq1gDW91POn6sCx7AIitFBep3M2NM9kN7J/MSCt7nphgj8TcEpn6C0m6XA== X-Gm-Gg: ASbGncuFMQBBzCVCvXskGHjSb1dLWBP9B6vXqb29fcGhJYDwyz0UiyN8IG9FtLmwp+j JgKow1+3peSKg7TlPU77pEIS3WloZL2x2UFIut5SG7tWhmKzMnQbF9QzdRx0Jn9EYpCAHCoP8fA XZFJDvzI7F2zJ0+ytRSg9otvlpHfTEDA7+skss8xyHl6f9iQ2oyDdUv+emyQyahUfq/oaemvQXz iX8rZijLiKnATJZpfcOOh1NOTQlA0dV4uPgnE+mhjS2ZyP1Eft5ZsyHyTgW8nqU+u+QRsM7p/c5 C3Awu2Ka0zHwCKaHp3j2XnUfPgXoW2YevAFgAvklhdUGSrg3DW2qz/wnU8MIXCFmMsrL0qIWatC H2G5aoJw4KLyk70nm5szuae8qydMMFTOdKRa921IZs584xE14SrjZfyW+EVsCzuEZIey4 X-Received: by 2002:a05:600c:a43:b0:45d:cfee:7058 with SMTP id 5b1f17b1804b1-46e329e4aa5mr41391075e9.22.1758828530782; Thu, 25 Sep 2025 12:28:50 -0700 (PDT) X-Google-Smtp-Source: AGHT+IEdB5XKgMH2Lxe6a6vu2Xy7Adch2dis5Y1Fy7OCZ/mT526GuwLzR5bO47EzrRa1c7ysWrxW0w== X-Received: by 2002:a05:600c:a43:b0:45d:cfee:7058 with SMTP id 5b1f17b1804b1-46e329e4aa5mr41390605e9.22.1758828530238; Thu, 25 Sep 2025 12:28:50 -0700 (PDT) Received: from ?IPV6:2003:d8:2f3f:f800:c101:5c9f:3bc9:3d08? (p200300d82f3ff800c1015c9f3bc93d08.dip0.t-ipconnect.de. [2003:d8:2f3f:f800:c101:5c9f:3bc9:3d08]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-40fc749b8f9sm3988405f8f.50.2025.09.25.12.28.47 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 25 Sep 2025 12:28:49 -0700 (PDT) Message-ID: Date: Thu, 25 Sep 2025 21:28:46 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v7 05/12] KVM: guest_memfd: Add flag to remove from direct map To: "Roy, Patrick" Cc: "Liam.Howlett@oracle.com" , "ackerleytng@google.com" , "akpm@linux-foundation.org" , "andrii@kernel.org" , "ast@kernel.org" , "bp@alien8.de" , "bpf@vger.kernel.org" , "catalin.marinas@arm.com" , "corbet@lwn.net" , "daniel@iogearbox.net" , "dave.hansen@linux.intel.com" , "derekmn@amazon.co.uk" , "eddyz87@gmail.com" , "haoluo@google.com" , "hpa@zytor.com" , "Thomson, Jack" , "jannh@google.com" , "jgg@ziepe.ca" , "jhubbard@nvidia.com" , "joey.gouly@arm.com" , "john.fastabend@gmail.com" , "jolsa@kernel.org" , "Kalyazin, Nikita" , "kpsingh@kernel.org" , "kvm@vger.kernel.org" , "kvmarm@lists.linux.dev" , "linux-arm-kernel@lists.infradead.org" , "linux-doc@vger.kernel.org" , "linux-fsdevel@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "linux-kselftest@vger.kernel.org" , "linux-mm@kvack.org" , "lorenzo.stoakes@oracle.com" , "luto@kernel.org" , "martin.lau@linux.dev" , "maz@kernel.org" , "mhocko@suse.com" , "mingo@redhat.com" , "oliver.upton@linux.dev" , "pbonzini@redhat.com" , "peterx@redhat.com" , "peterz@infradead.org" , "pfalcato@suse.de" , "rppt@kernel.org" , "sdf@fomichev.me" , "seanjc@google.com" , "shuah@kernel.org" , "song@kernel.org" , "surenb@google.com" , "suzuki.poulose@arm.com" , "tabba@google.com" , "tglx@linutronix.de" , "vbabka@suse.cz" , "will@kernel.org" , "willy@infradead.org" , "x86@kernel.org" , "Cali, Marco" , "yonghong.song@linux.dev" , "yuzenghui@huawei.com" References: <20250925155237.3928-1-roypat@amazon.co.uk> From: David Hildenbrand Content-Language: en-US Autocrypt: addr=david@redhat.com; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzSREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZoEEwEIAEQCGwMCF4ACGQEFCwkIBwICIgIG FQoJCAsCBBYCAwECHgcWIQQb2cqtc1xMOkYN/MpN3hD3AP+DWgUCaJzangUJJlgIpAAKCRBN 3hD3AP+DWhAxD/9wcL0A+2rtaAmutaKTfxhTP0b4AAp1r/eLxjrbfbCCmh4pqzBhmSX/4z11 opn2KqcOsueRF1t2ENLOWzQu3Roiny2HOU7DajqB4dm1BVMaXQya5ae2ghzlJN9SIoopTWlR 0Af3hPj5E2PYvQhlcqeoehKlBo9rROJv/rjmr2x0yOM8qeTroH/ZzNlCtJ56AsE6Tvl+r7cW 3x7/Jq5WvWeudKrhFh7/yQ7eRvHCjd9bBrZTlgAfiHmX9AnCCPRPpNGNedV9Yty2Jnxhfmbv Pw37LA/jef8zlCDyUh2KCU1xVEOWqg15o1RtTyGV1nXV2O/mfuQJud5vIgzBvHhypc3p6VZJ lEf8YmT+Ol5P7SfCs5/uGdWUYQEMqOlg6w9R4Pe8d+mk8KGvfE9/zTwGg0nRgKqlQXrWRERv cuEwQbridlPAoQHrFWtwpgYMXx2TaZ3sihcIPo9uU5eBs0rf4mOERY75SK+Ekayv2ucTfjxr Kf014py2aoRJHuvy85ee/zIyLmve5hngZTTe3Wg3TInT9UTFzTPhItam6dZ1xqdTGHZYGU0O otRHcwLGt470grdiob6PfVTXoHlBvkWRadMhSuG4RORCDpq89vu5QralFNIf3EysNohoFy2A LYg2/D53xbU/aa4DDzBb5b1Rkg/udO1gZocVQWrDh6I2K3+cCs7BTQRVy5+RARAA59fefSDR 9nMGCb9LbMX+TFAoIQo/wgP5XPyzLYakO+94GrgfZjfhdaxPXMsl2+o8jhp/hlIzG56taNdt VZtPp3ih1AgbR8rHgXw1xwOpuAd5lE1qNd54ndHuADO9a9A0vPimIes78Hi1/yy+ZEEvRkHk /kDa6F3AtTc1m4rbbOk2fiKzzsE9YXweFjQvl9p+AMw6qd/iC4lUk9g0+FQXNdRs+o4o6Qvy iOQJfGQ4UcBuOy1IrkJrd8qq5jet1fcM2j4QvsW8CLDWZS1L7kZ5gT5EycMKxUWb8LuRjxzZ 3QY1aQH2kkzn6acigU3HLtgFyV1gBNV44ehjgvJpRY2cC8VhanTx0dZ9mj1YKIky5N+C0f21 zvntBqcxV0+3p8MrxRRcgEtDZNav+xAoT3G0W4SahAaUTWXpsZoOecwtxi74CyneQNPTDjNg azHmvpdBVEfj7k3p4dmJp5i0U66Onmf6mMFpArvBRSMOKU9DlAzMi4IvhiNWjKVaIE2Se9BY FdKVAJaZq85P2y20ZBd08ILnKcj7XKZkLU5FkoA0udEBvQ0f9QLNyyy3DZMCQWcwRuj1m73D sq8DEFBdZ5eEkj1dCyx+t/ga6x2rHyc8Sl86oK1tvAkwBNsfKou3v+jP/l14a7DGBvrmlYjO 59o3t6inu6H7pt7OL6u6BQj7DoMAEQEAAcLBfAQYAQgAJgIbDBYhBBvZyq1zXEw6Rg38yk3e EPcA/4NaBQJonNqrBQkmWAihAAoJEE3eEPcA/4NaKtMQALAJ8PzprBEXbXcEXwDKQu+P/vts IfUb1UNMfMV76BicGa5NCZnJNQASDP/+bFg6O3gx5NbhHHPeaWz/VxlOmYHokHodOvtL0WCC 8A5PEP8tOk6029Z+J+xUcMrJClNVFpzVvOpb1lCbhjwAV465Hy+NUSbbUiRxdzNQtLtgZzOV Zw7jxUCs4UUZLQTCuBpFgb15bBxYZ/BL9MbzxPxvfUQIPbnzQMcqtpUs21CMK2PdfCh5c4gS sDci6D5/ZIBw94UQWmGpM/O1ilGXde2ZzzGYl64glmccD8e87OnEgKnH3FbnJnT4iJchtSvx yJNi1+t0+qDti4m88+/9IuPqCKb6Stl+s2dnLtJNrjXBGJtsQG/sRpqsJz5x1/2nPJSRMsx9 5YfqbdrJSOFXDzZ8/r82HgQEtUvlSXNaXCa95ez0UkOG7+bDm2b3s0XahBQeLVCH0mw3RAQg r7xDAYKIrAwfHHmMTnBQDPJwVqxJjVNr7yBic4yfzVWGCGNE4DnOW0vcIeoyhy9vnIa3w1uZ 3iyY2Nsd7JxfKu1PRhCGwXzRw5TlfEsoRI7V9A8isUCoqE2Dzh3FvYHVeX4Us+bRL/oqareJ CIFqgYMyvHj7Q06kTKmauOe4Nf0l0qEkIuIzfoLJ3qr5UyXc2hLtWyT9Ir+lYlX9efqh7mOY qIws/H2t In-Reply-To: <20250925155237.3928-1-roypat@amazon.co.uk> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 25.09.25 17:52, Roy, Patrick wrote: > On Thu, 2025-09-25 at 12:00 +0100, David Hildenbrand wrote: >> On 24.09.25 17:22, Roy, Patrick wrote: >>> Add GUEST_MEMFD_FLAG_NO_DIRECT_MAP flag for KVM_CREATE_GUEST_MEMFD() >>> ioctl. When set, guest_memfd folios will be removed from the direct map >>> after preparation, with direct map entries only restored when the folios >>> are freed. >>> >>> To ensure these folios do not end up in places where the kernel cannot >>> deal with them, set AS_NO_DIRECT_MAP on the guest_memfd's struct >>> address_space if GUEST_MEMFD_FLAG_NO_DIRECT_MAP is requested. >>> >>> Add KVM_CAP_GUEST_MEMFD_NO_DIRECT_MAP to let userspace discover whether >>> guest_memfd supports GUEST_MEMFD_FLAG_NO_DIRECT_MAP. Support depends on >>> guest_memfd itself being supported, but also on whether linux supports >>> manipulatomg the direct map at page granularity at all (possible most of >>> the time, outliers being arm64 where its impossible if the direct map >>> has been setup using hugepages, as arm64 cannot break these apart due to >>> break-before-make semantics, and powerpc, which does not select >>> ARCH_HAS_SET_DIRECT_MAP, though also doesn't support guest_memfd >>> anyway). >>> >>> Note that this flag causes removal of direct map entries for all >>> guest_memfd folios independent of whether they are "shared" or "private" >>> (although current guest_memfd only supports either all folios in the >>> "shared" state, or all folios in the "private" state if >>> GUEST_MEMFD_FLAG_MMAP is not set). The usecase for removing direct map >>> entries of also the shared parts of guest_memfd are a special type of >>> non-CoCo VM where, host userspace is trusted to have access to all of >>> guest memory, but where Spectre-style transient execution attacks >>> through the host kernel's direct map should still be mitigated. In this >>> setup, KVM retains access to guest memory via userspace mappings of >>> guest_memfd, which are reflected back into KVM's memslots via >>> userspace_addr. This is needed for things like MMIO emulation on x86_64 >>> to work. >>> >>> Direct map entries are zapped right before guest or userspace mappings >>> of gmem folios are set up, e.g. in kvm_gmem_fault_user_mapping() or >>> kvm_gmem_get_pfn() [called from the KVM MMU code]. The only place where >>> a gmem folio can be allocated without being mapped anywhere is >>> kvm_gmem_populate(), where handling potential failures of direct map >>> removal is not possible (by the time direct map removal is attempted, >>> the folio is already marked as prepared, meaning attempting to re-try >>> kvm_gmem_populate() would just result in -EEXIST without fixing up the >>> direct map state). These folios are then removed form the direct map >>> upon kvm_gmem_get_pfn(), e.g. when they are mapped into the guest later. >>> >>> Signed-off-by: Patrick Roy >>> --- >>> Documentation/virt/kvm/api.rst | 5 +++ >>> arch/arm64/include/asm/kvm_host.h | 12 ++++++ >>> include/linux/kvm_host.h | 6 +++ >>> include/uapi/linux/kvm.h | 2 + >>> virt/kvm/guest_memfd.c | 61 ++++++++++++++++++++++++++++++- >>> virt/kvm/kvm_main.c | 5 +++ >>> 6 files changed, 90 insertions(+), 1 deletion(-) >>> >>> diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst >>> index c17a87a0a5ac..b52c14d58798 100644 >>> --- a/Documentation/virt/kvm/api.rst >>> +++ b/Documentation/virt/kvm/api.rst >>> @@ -6418,6 +6418,11 @@ When the capability KVM_CAP_GUEST_MEMFD_MMAP is supported, the 'flags' field >>> supports GUEST_MEMFD_FLAG_MMAP. Setting this flag on guest_memfd creation >>> enables mmap() and faulting of guest_memfd memory to host userspace. >>> >>> +When the capability KVM_CAP_GMEM_NO_DIRECT_MAP is supported, the 'flags' field >>> +supports GUEST_MEMFG_FLAG_NO_DIRECT_MAP. Setting this flag makes the guest_memfd >>> +instance behave similarly to memfd_secret, and unmaps the memory backing it from >>> +the kernel's address space after allocation. >>> + >> >> Do we want to document what the implication of that is? Meaning, >> limitations etc. I recall that we would need the user mapping for gmem >> slots to be properly set up. >> >> Is that still the case in this patch set? > > The ->userspace_addr thing is the general requirement for non-CoCo VMs, > and not specific for direct map removal (e.g. I expect direct map > removal to just work out of the box for CoCo setups, where KVM already > cannot access guest memory, ignoring the question of whether direct map > removal is even useful for CoCo VMs). So I don't think it should be > documented as part of > KVM_CAP_GMEM_NO_DIRECT_MAP/GUEST_MEMFG_FLAG_NO_DIRECT_MAP (heh, there's > a typo I just noticed. Okay I was rather wondering whether this will be the first patch set where it is actually required to be set. In the basic mmap series, I am not sure yet if we really depend on it (but IIRC we did document it, but do no sanity checks etc). "MEMFG". Also "GMEM" needs to be "GUEST_MEMFD". > Will fix that), but rather as part of GUEST_MEMFD_FLAG_MMAP. I can add a > patch it there (or maybe send it separately, since FLAG_MMAP is already > in -next?). Yes, it's in kvm/next and will go upstream soon. > >>> When the KVM MMU performs a PFN lookup to service a guest fault and the backing >>> guest_memfd has the GUEST_MEMFD_FLAG_MMAP set, then the fault will always be >>> consumed from guest_memfd, regardless of whether it is a shared or a private >>> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h >>> index 2f2394cce24e..0bfd8e5fd9de 100644 >>> --- a/arch/arm64/include/asm/kvm_host.h >>> +++ b/arch/arm64/include/asm/kvm_host.h >>> @@ -19,6 +19,7 @@ >>> #include >>> #include >>> #include >>> +#include >>> #include >>> #include >>> #include >>> @@ -1706,5 +1707,16 @@ void compute_fgu(struct kvm *kvm, enum fgt_group_id fgt); >>> void get_reg_fixed_bits(struct kvm *kvm, enum vcpu_sysreg reg, u64 *res0, u64 *res1); >>> void check_feature_map(void); >>> >>> +#ifdef CONFIG_KVM_GUEST_MEMFD >>> +static inline bool kvm_arch_gmem_supports_no_direct_map(void) >>> +{ >>> + /* >>> + * Without FWB, direct map access is needed in kvm_pgtable_stage2_map(), >>> + * as it calls dcache_clean_inval_poc(). >>> + */ >>> + return can_set_direct_map() && cpus_have_final_cap(ARM64_HAS_STAGE2_FWB); >>> +} >>> +#define kvm_arch_gmem_supports_no_direct_map kvm_arch_gmem_supports_no_direct_map >>> +#endif /* CONFIG_KVM_GUEST_MEMFD */ >>> >> >> I strongly assume that the aarch64 support should be moved to a separate >> patch -- if possible, see below. >> >>> #endif /* __ARM64_KVM_HOST_H__ */ >>> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h >>> index 1d0585616aa3..73a15cade54a 100644 >>> --- a/include/linux/kvm_host.h >>> +++ b/include/linux/kvm_host.h >>> @@ -731,6 +731,12 @@ static inline bool kvm_arch_has_private_mem(struct kvm *kvm) >>> bool kvm_arch_supports_gmem_mmap(struct kvm *kvm); >>> #endif >>> >>> +#ifdef CONFIG_KVM_GUEST_MEMFD >>> +#ifndef kvm_arch_gmem_supports_no_direct_map >>> +#define kvm_arch_gmem_supports_no_direct_map can_set_direct_map >>> +#endif >> >> Hm, wouldn't it be better to have an opt-in per arch, and really only >> unlock the ones we know work (tested etc), explicitly in separate patches. >> > > Ack, can definitely do that. Something like > > #ifndef kvm_arch_gmem_supports_no_direct_map > static inline bool kvm_arch_gmem_supports_no_direct_map() > { > return false; > } > #endif > > and then actual definitions (in separate patches) in the arm64 and x86 > headers? > > On a related note, maybe PATCH 2 should only export > set_direct_map_valid_noflush() for the architectures on which we > actually need it? Which would only be x86, since arm64 doesnt allow > building KVM as a module, and nothing else supports guest_memfd right > now. Yes, that's probably best. Could be done in the same arch patch then. -- Cheers David / dhildenb