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keydata= xjMEY0UgYhYJKwYBBAHaRw8BAQdA7lj+ADr5b96qBcdINFVJSOg8RGtKthL5x77F2ABMh4PN NVBhdHJpY2sgUm95IChHaXRodWIga2V5IGFtYXpvbikgPHJveXBhdEBhbWF6b24uY28udWs+ wpMEExYKADsWIQQ5DAcjaM+IvmZPLohVg4tqeAbEAgUCY0UgYgIbAwULCQgHAgIiAgYVCgkI CwIEFgIDAQIeBwIXgAAKCRBVg4tqeAbEAmQKAQC1jMl/KT9pQHEdALF7SA1iJ9tpA5ppl1J9 AOIP7Nr9SwD/fvIWkq0QDnq69eK7HqW14CA7AToCF6NBqZ8r7ksi+QLOOARjRSBiEgorBgEE AZdVAQUBAQdAqoMhGmiXJ3DMGeXrlaDA+v/aF/ah7ARbFV4ukHyz+CkDAQgHwngEGBYKACAW IQQ5DAcjaM+IvmZPLohVg4tqeAbEAgUCY0UgYgIbDAAKCRBVg4tqeAbEAtjHAQDkh5jZRIsZ 7JMNkPMSCd5PuSy0/Gdx8LGgsxxPMZwePgEAn5Tnh4fVbf00esnoK588bYQgJBioXtuXhtom 8hlxFQM= In-Reply-To: Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 7276F4001F X-Stat-Signature: 6xk87qj9k3q1g6w6efzi7n4wsws1pnx9 X-Rspam-User: X-Rspamd-Server: rspam05 X-HE-Tag: 1731689916-378099 X-HE-Meta: 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 0+jKDxBK 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000004, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, 2024-11-12 at 14:52 +0000, David Hildenbrand wrote: > On 12.11.24 15:40, Patrick Roy wrote: >> I remember talking to someone at some point about whether we could reuse >> the proc-local stuff for guest memory, but I cannot remember the outcome >> of that discussion... (or maybe I just wanted to have a discussion about >> it, but forgot to follow up on that thought?). I guess we wouldn't use >> proc-local _allocations_, but rather just set up proc-local mappings of >> the gmem allocations that have been removed from the direct map. > > Yes. And likely only for memory we really access / try access, if possible. Well, if we start on-demand mm-local mapping the things we want to access, we're back in TLB flush hell, no? And we can't know ahead-of-time what needs to be mapped, so everything would need to be mapped (unless we do something like mm-local mapping a page on first access, and then just never unmapping it again, under the assumption that establishing the mapping won't be expensive) >> >> I'm wondering, where exactly would be the differences to Sean's idea >> about messing with the CR3 register inside KVM to temporarily install >> page tables that contain all the gmem stuff, conceptually? Wouldn't we >> run into the same interrupt problems that Sean foresaw for the CR3 >> stuff? (which, admittedly, I still don't quite follow what these are :( >> ). > > I'd need some more details on that. If anything would rely on the direct > mapping (from IRQ context?) than ... we obviously cannot remove the > direct mapping :) I've talked to Fares internally, and it seems that generally doing mm-local mappings of guest memory would work for us. We also figured out what the "interrupt problem" is, namely that if we receive an interrupt while executing in a context that has mm-local mappings available, those mappings will continue to be available while the interrupt is being handled. I'm talking to my security folks to see how much of a concern this is for the speculation hardening we're trying to achieve. Will keep you in the loop there :) > -- > Cheers, > > David / dhildenb > Best, Patrick