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[2003:cb:c709:6200:16ba:af70:999d:6a1a]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-437c753bee8sm251379565e9.34.2025.01.21.10.24.29 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 21 Jan 2025 10:24:30 -0800 (PST) Message-ID: Date: Tue, 21 Jan 2025 19:24:29 +0100 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 v3 07/49] HostMem: Add mechanism to opt in kvm guest memfd via MachineState To: Peter Xu , Michael Roth Cc: qemu-devel@nongnu.org, kvm@vger.kernel.org, Tom Lendacky , Paolo Bonzini , =?UTF-8?Q?Daniel_P=2E_Berrang=C3=A9?= , Markus Armbruster , Pankaj Gupta , Xiaoyao Li , Isaku Yamahata References: <20240320083945.991426-1-michael.roth@amd.com> <20240320083945.991426-8-michael.roth@amd.com> 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 ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZgEEwEIAEICGwMGCwkIBwMCBhUIAgkKCwQW AgMBAh4BAheAAhkBFiEEG9nKrXNcTDpGDfzKTd4Q9wD/g1oFAl8Ox4kFCRKpKXgACgkQTd4Q 9wD/g1oHcA//a6Tj7SBNjFNM1iNhWUo1lxAja0lpSodSnB2g4FCZ4R61SBR4l/psBL73xktp rDHrx4aSpwkRP6Epu6mLvhlfjmkRG4OynJ5HG1gfv7RJJfnUdUM1z5kdS8JBrOhMJS2c/gPf wv1TGRq2XdMPnfY2o0CxRqpcLkx4vBODvJGl2mQyJF/gPepdDfcT8/PY9BJ7FL6Hrq1gnAo4 3Iv9qV0JiT2wmZciNyYQhmA1V6dyTRiQ4YAc31zOo2IM+xisPzeSHgw3ONY/XhYvfZ9r7W1l pNQdc2G+o4Di9NPFHQQhDw3YTRR1opJaTlRDzxYxzU6ZnUUBghxt9cwUWTpfCktkMZiPSDGd KgQBjnweV2jw9UOTxjb4LXqDjmSNkjDdQUOU69jGMUXgihvo4zhYcMX8F5gWdRtMR7DzW/YE BgVcyxNkMIXoY1aYj6npHYiNQesQlqjU6azjbH70/SXKM5tNRplgW8TNprMDuntdvV9wNkFs 9TyM02V5aWxFfI42+aivc4KEw69SE9KXwC7FSf5wXzuTot97N9Phj/Z3+jx443jo2NR34XgF 89cct7wJMjOF7bBefo0fPPZQuIma0Zym71cP61OP/i11ahNye6HGKfxGCOcs5wW9kRQEk8P9 M/k2wt3mt/fCQnuP/mWutNPt95w9wSsUyATLmtNrwccz63XOwU0EVcufkQEQAOfX3n0g0fZz Bgm/S2zF/kxQKCEKP8ID+Vz8sy2GpDvveBq4H2Y34XWsT1zLJdvqPI4af4ZSMxuerWjXbVWb T6d4odQIG0fKx4F8NccDqbgHeZRNajXeeJ3R7gAzvWvQNLz4piHrO/B4tf8svmRBL0ZB5P5A 2uhdwLU3NZuK22zpNn4is87BPWF8HhY0L5fafgDMOqnf4guJVJPYNPhUFzXUbPqOKOkL8ojk CXxkOFHAbjstSK5Ca3fKquY3rdX3DNo+EL7FvAiw1mUtS+5GeYE+RMnDCsVFm/C7kY8c2d0G NWkB9pJM5+mnIoFNxy7YBcldYATVeOHoY4LyaUWNnAvFYWp08dHWfZo9WCiJMuTfgtH9tc75 7QanMVdPt6fDK8UUXIBLQ2TWr/sQKE9xtFuEmoQGlE1l6bGaDnnMLcYu+Asp3kDT0w4zYGsx 5r6XQVRH4+5N6eHZiaeYtFOujp5n+pjBaQK7wUUjDilPQ5QMzIuCL4YjVoylWiBNknvQWBXS lQCWmavOT9sttGQXdPCC5ynI+1ymZC1ORZKANLnRAb0NH/UCzcsstw2TAkFnMEbo9Zu9w7Kv AxBQXWeXhJI9XQssfrf4Gusdqx8nPEpfOqCtbbwJMATbHyqLt7/oz/5deGuwxgb65pWIzufa N7eop7uh+6bezi+rugUI+w6DABEBAAHCwXwEGAEIACYCGwwWIQQb2cqtc1xMOkYN/MpN3hD3 AP+DWgUCXw7HsgUJEqkpoQAKCRBN3hD3AP+DWrrpD/4qS3dyVRxDcDHIlmguXjC1Q5tZTwNB boaBTPHSy/Nksu0eY7x6HfQJ3xajVH32Ms6t1trDQmPx2iP5+7iDsb7OKAb5eOS8h+BEBDeq 3ecsQDv0fFJOA9ag5O3LLNk+3x3q7e0uo06XMaY7UHS341ozXUUI7wC7iKfoUTv03iO9El5f XpNMx/YrIMduZ2+nd9Di7o5+KIwlb2mAB9sTNHdMrXesX8eBL6T9b+MZJk+mZuPxKNVfEQMQ a5SxUEADIPQTPNvBewdeI80yeOCrN+Zzwy/Mrx9EPeu59Y5vSJOx/z6OUImD/GhX7Xvkt3kq Er5KTrJz3++B6SH9pum9PuoE/k+nntJkNMmQpR4MCBaV/J9gIOPGodDKnjdng+mXliF3Ptu6 3oxc2RCyGzTlxyMwuc2U5Q7KtUNTdDe8T0uE+9b8BLMVQDDfJjqY0VVqSUwImzTDLX9S4g/8 kC4HRcclk8hpyhY2jKGluZO0awwTIMgVEzmTyBphDg/Gx7dZU1Xf8HFuE+UZ5UDHDTnwgv7E th6RC9+WrhDNspZ9fJjKWRbveQgUFCpe1sa77LAw+XFrKmBHXp9ZVIe90RMe2tRL06BGiRZr jPrnvUsUUsjRoRNJjKKA/REq+sAnhkNPPZ/NNMjaZ5b8Tovi8C0tmxiCHaQYqj7G2rgnT0kt WNyWQQ== Organization: Red Hat In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 21.01.25 18:39, Peter Xu wrote: > On Wed, Mar 20, 2024 at 03:39:03AM -0500, Michael Roth wrote: >> From: Xiaoyao Li >> >> Add a new member "guest_memfd" to memory backends. When it's set >> to true, it enables RAM_GUEST_MEMFD in ram_flags, thus private kvm >> guest_memfd will be allocated during RAMBlock allocation. >> >> Memory backend's @guest_memfd is wired with @require_guest_memfd >> field of MachineState. It avoid looking up the machine in phymem.c. >> >> MachineState::require_guest_memfd is supposed to be set by any VMs >> that requires KVM guest memfd as private memory, e.g., TDX VM. >> >> Signed-off-by: Xiaoyao Li >> Reviewed-by: David Hildenbrand >> --- >> Changes in v4: >> - rename "require_guest_memfd" to "guest_memfd" in struct >> HostMemoryBackend; (David Hildenbrand) >> Signed-off-by: Michael Roth >> --- >> backends/hostmem-file.c | 1 + >> backends/hostmem-memfd.c | 1 + >> backends/hostmem-ram.c | 1 + >> backends/hostmem.c | 1 + >> hw/core/machine.c | 5 +++++ >> include/hw/boards.h | 2 ++ >> include/sysemu/hostmem.h | 1 + >> 7 files changed, 12 insertions(+) >> >> diff --git a/backends/hostmem-file.c b/backends/hostmem-file.c >> index ac3e433cbd..3c69db7946 100644 >> --- a/backends/hostmem-file.c >> +++ b/backends/hostmem-file.c >> @@ -85,6 +85,7 @@ file_backend_memory_alloc(HostMemoryBackend *backend, Error **errp) >> ram_flags |= fb->readonly ? RAM_READONLY_FD : 0; >> ram_flags |= fb->rom == ON_OFF_AUTO_ON ? RAM_READONLY : 0; >> ram_flags |= backend->reserve ? 0 : RAM_NORESERVE; >> + ram_flags |= backend->guest_memfd ? RAM_GUEST_MEMFD : 0; >> ram_flags |= fb->is_pmem ? RAM_PMEM : 0; >> ram_flags |= RAM_NAMED_FILE; >> return memory_region_init_ram_from_file(&backend->mr, OBJECT(backend), name, >> diff --git a/backends/hostmem-memfd.c b/backends/hostmem-memfd.c >> index 3923ea9364..745ead0034 100644 >> --- a/backends/hostmem-memfd.c >> +++ b/backends/hostmem-memfd.c >> @@ -55,6 +55,7 @@ memfd_backend_memory_alloc(HostMemoryBackend *backend, Error **errp) >> name = host_memory_backend_get_name(backend); >> ram_flags = backend->share ? RAM_SHARED : 0; >> ram_flags |= backend->reserve ? 0 : RAM_NORESERVE; >> + ram_flags |= backend->guest_memfd ? RAM_GUEST_MEMFD : 0; >> return memory_region_init_ram_from_fd(&backend->mr, OBJECT(backend), name, >> backend->size, ram_flags, fd, 0, errp); >> } >> diff --git a/backends/hostmem-ram.c b/backends/hostmem-ram.c >> index d121249f0f..f7d81af783 100644 >> --- a/backends/hostmem-ram.c >> +++ b/backends/hostmem-ram.c >> @@ -30,6 +30,7 @@ ram_backend_memory_alloc(HostMemoryBackend *backend, Error **errp) >> name = host_memory_backend_get_name(backend); >> ram_flags = backend->share ? RAM_SHARED : 0; >> ram_flags |= backend->reserve ? 0 : RAM_NORESERVE; >> + ram_flags |= backend->guest_memfd ? RAM_GUEST_MEMFD : 0; >> return memory_region_init_ram_flags_nomigrate(&backend->mr, OBJECT(backend), >> name, backend->size, >> ram_flags, errp); > > These change look a bit confusing to me, as I don't see how gmemfd can be > used with either file or ram typed memory backends.. I recall that the following should work: "private" memory will come from guest_memfd, "shared" (as in, accessible by the host) will come from anonymous memory. This "anon" memory cannot be "shared" with other processes, but virtio-kernel etc. can just use it. To "share" the memory with other processes, we'd need memfd/file. > > When specified gmemfd=on with those, IIUC it'll allocate both the memory > (ramblock->host) and gmemfd, but without using ->host. Meanwhile AFAIU the > ramblock->host will start to conflict with gmemfd in the future when it > might be able to be mapp-able (having valid ->host). These will require a new guest_memfd memory backend (I recall that was discussed a couple of times). > > I have a local fix for this (and actually more than below.. but starting > from it), I'm not sure whether I overlooked something, but from reading the > cover letter it's only using memfd backend which makes perfect sense to me > so far. Does the anon+guest_memfd combination not work or are you speculating about the usability (which I hopefully addressed above). -- Cheers, David / dhildenb