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([2600:1700:38d4:55d0:d0ab:d0aa:3b14:767a]) by smtp.gmail.com with ESMTPSA id 41be03b00d2f7-af56e9dd388sm9562322a12.20.2025.03.18.15.48.48 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 18 Mar 2025 15:48:49 -0700 (PDT) Message-ID: <14f9106d-3a34-4f10-ba4e-465c73c94eba@google.com> Date: Tue, 18 Mar 2025 15:48:47 -0700 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH RFC v2 03/29] mm: asi: Introduce ASI core API To: Brendan Jackman , Borislav Petkov Cc: akpm@linux-foundation.org, dave.hansen@linux.intel.com, yosryahmed@google.com, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, peterz@infradead.org, seanjc@google.com, tglx@linutronix.de, x86@kernel.org References: <20250227120607.GPZ8BVL2762we1j3uE@fat_crate.local> <20250228084355.2061899-1-jackmanb@google.com> <20250314131419.GJZ9Qrq8scAtDyBUcg@fat_crate.local> <5aa114f7-3efb-4dab-8579-cb9af4abd3c0@google.com> <20250315123621.GCZ9V0RWGFapbQNL1w@fat_crate.local> <4ce0b11c-d2fd-4dff-b9db-30e50500ee83@google.com> Content-Language: en-US From: Junaid Shahid In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Queue-Id: E49D91C000D X-Rspamd-Server: rspam08 X-Stat-Signature: 1joo8d96wdwq1pra5qsxhgthm51wffm6 X-HE-Tag: 1742338131-517352 X-HE-Meta: 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 mS438MO7 OSfCl8T14Xp/Td/tbb8U2h1bui/UQB/1QZmJgdzL+jpoxgKMfpdpC5ShiPfEYJgckPIUJ+4meOgugobwlCvAurvyhc8zGCs5+0YKuVPT+CkXnGUgthjZ1fDP5z6GAj7ZpVLkMWuFwUCcn10Lxl0kVhdr2bXAjIMcxsb3DOo7BjI6/FFQEDL++7InRjbyMEEsP3Vo21rBgO63eMtyD/opkefF5UE+BanvScNTryKEk3YbfM0aj4feH8QS+vXCmPOJ99DJvV+oHAxHicPWhiZ/d9YX+htQnw++xInG34oOU6i0fTJWO9CQPUPVDT0YmtXfWEZLS5GHWZQKP3FvKIvik6s/XBcF4fxHyYF1VitLsb+SQPjl7xuAIpZ8r2Q== X-Bogosity: Ham, tests=bogofilter, spamicity=0.000060, 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 3/18/25 6:03 AM, Brendan Jackman wrote: > On Tue Mar 18, 2025 at 12:50 AM UTC, Junaid Shahid wrote: >> On 3/17/25 4:40 AM, Brendan Jackman wrote: >>> >>> static inline void asi_start(void) >>> { >>> /* >>> * Cannot currently context switch in the restricted adddress >>> * space. >>> */ >>> lockdep_assert_preemption_disabled(); >> >> I assume that this limitation is just for the initial version in this RFC, >> right? > > Well I think we also wanna get ASI in-tree with this limitation, > otherwise the initial series will be too big and complex. Agreed. That is what I meant as well. > >> But even in that case, I think this should be in asi_start_critical() >> below, not asi_start(), since IIRC the KVM run loop does contain preemptible >> code as well. And we would need an explicit asi_exit() in the context switch >> code like we had in an earlier RFC. > > Oh. Yeah. In my proposal below I had totally forgotten we had > asi_exit() in the context_switch() path (it is there in this patch). > > So we only need the asi_exit() in the KVM code in order to avoid > actually hitting e.g. exit_to_user_mode() in the restricted address > space. > > But... we can just put an asi_exit() there explicitly instead of > dumping all this weirdness into the "core API" and the KVM codebase. > > So... I think all we really need is asi_start_critical() and > asi_end_critical()? And make everything else happen as part of the > normal functioning of the entry and context-switching logic. Am I > forgetting something else? Yes, I think this should work. Thanks, Junaid