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To: Dave Hansen , tglx@kernel.org, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org, hpa@zytor.com, seanjc@google.com, peterz@infradead.org, thomas.lendacky@amd.com, herbert@gondor.apana.org.au, davem@davemloft.net, ardb@kernel.org Cc: pbonzini@redhat.com, aik@amd.com, Michael.Roth@amd.com, KPrateek.Nayak@amd.com, Tycho.Andersen@amd.com, Nathan.Fontenot@amd.com, jackyli@google.com, pgonda@google.com, rientjes@google.com, jacobhxu@google.com, xin@zytor.com, pawan.kumar.gupta@linux.intel.com, babu.moger@amd.com, dyoung@redhat.com, nikunj@amd.com, john.allen@amd.com, darwi@linutronix.de, linux-kernel@vger.kernel.org, linux-crypto@vger.kernel.org, kvm@vger.kernel.org, linux-coco@lists.linux.dev References: <88ddc178dcab3d27d6296e471218f13a4826f4a8.1771321114.git.ashish.kalra@amd.com> <21250a3e-536c-4348-bf4c-a7356a13939b@intel.com> Content-Language: en-US From: "Kalra, Ashish" In-Reply-To: <21250a3e-536c-4348-bf4c-a7356a13939b@intel.com> Content-Type: text/plain; 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Therefore, an interface is required to manually >> re-enable RMP optimizations, as no mechanism currently exists to do so >> during SNP guest cleanup. > > Is this like a proof-of-concept to poke the hardware and show it works? > Or, is this intended to be the way that folks actually interact with > SEV-SNP optimization in real production scenarios? > > Shouldn't freeing SEV-SNP memory back to the system do this > automatically? Worst case, keep a 1-bit-per-GB bitmap of memory that's > been freed and schedule_work() to run in 1 or 10 or 100 seconds. That > should batch things up nicely enough. No? Actually, the RMPOPT implementation is going to be a multi-phased development. In the first phase (which is this patch-series) we enable RMPOPT globally, and let RMPUPDATE(s) slowly switch it off over time as SNP guest spin up, and then in phase#2 once 1GB hugetlb is in place, we enable re-issuing of RMPOPT during 1GB page cleanup. So automatic re-issuing of RMPOPT will be done when SNP guests are shutdown and as part of SNP guest cleanup once 1GB hugetlb support (for guest_memfd) has been merged. As currently, i.e, as part of this patch series, there is no mechanism to re-issue RMPOPT automatically as part of SNP guest cleanup, therefore this support exists to doing it manually at runtime via configfs. I will describe this multi-phased RMPOPT implementation plan in the cover letter for next revision of this patch series. Thanks, Ashish > > I can't fathom that users don't want this to be done automatically for them. > > Is the optimization scan really expensive or something? 1GB of memory > should have a small number of megabytes of metadata to scan.