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X-CSE-ConnectionGUID: Kt84rvcsQKeI0EhLgn03cw== X-CSE-MsgGUID: ZbqrkznfQ463wA01T9xuFg== X-IronPort-AV: E=McAfee;i="6800,10657,11733"; a="85591921" X-IronPort-AV: E=Sophos;i="6.23,127,1770624000"; d="scan'208";a="85591921" Received: from orviesa003.jf.intel.com ([10.64.159.143]) by fmvoesa103.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 18 Mar 2026 07:00:53 -0700 X-CSE-ConnectionGUID: veXwXH8MSBS3SbVil14Siw== X-CSE-MsgGUID: FHFSZgihSTObCHLOC37lyw== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.23,127,1770624000"; d="scan'208";a="226765480" Received: from rchatre-mobl4.amr.corp.intel.com (HELO [10.125.108.223]) ([10.125.108.223]) by ORVIESA003-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 18 Mar 2026 07:00:52 -0700 Message-ID: Date: Wed, 18 Mar 2026 07:00:51 -0700 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 v2 3/7] x86/sev: add support for RMPOPT instruction To: "Kalra, Ashish" , Sean Christopherson Cc: tglx@kernel.org, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org, hpa@zytor.com, peterz@infradead.org, thomas.lendacky@amd.com, herbert@gondor.apana.org.au, davem@davemloft.net, ardb@kernel.org, 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: <8dc0198f1261f5ae4b16388fc1ffad5ddb3895f9.1772486459.git.ashish.kalra@amd.com> <7ab8d3af-b4f5-481c-ab2e-059ddd7e718e@intel.com> <0fbb94ad-bfcf-4fbe-bf40-d79051d67ad8@amd.com> <6a4f4ecf-ffc0-43a9-98d4-06235b42063e@amd.com> <5102edd8-8eaa-4688-b3f7-3004c4cbc8f3@intel.com> Content-Language: en-US From: Dave Hansen Autocrypt: addr=dave.hansen@intel.com; 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charset=UTF-8 Content-Transfer-Encoding: 7bit Thanks for the additional performance numbers! On 3/16/26 12:03, Kalra, Ashish wrote: > Again, looking at the numbers above, what are your suggestions for > > 1). using the kthread approach OR I don't like the kthread approach. The kernel has a billion features. If each one gets a kthread or kthread-per-$SOMETHING, we'll spend all of our RAM on kthread task_structs and stacks. > 2). probably scheduling it for later execution after SNP guest termination via a workqueue OR I think there are two different issues: 1. What asynchronous kernel mechanism is used to execute the RMPOPT? 2. How does that mechanism get triggered? For #1, I think schedule_work() is the place to start. You need more justification on why it needs a dedicated kthread. For #2, I say just schedule some delayed work on every SEV-SNP private=>shared conversion to do RMPOPT. Schedule it out 1 second or 10 seconds or _something_. If work is scheduled and you convert another page, cancel it and push it out another 1 or 10 seconds. > 3). use some additional data structure like a bitmap to track 1G pages in guest_memfd > to do the RMP re-optimizations. That's an optimization that can be added later. Whatever you do, it's going to need trigger points and asynchronous work. There will always be ways to get the work amount down, but the worst case will always be there.