From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id A5C16C55ABF for ; Thu, 6 Aug 2026 13:20:22 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 3C2E36B007B; Thu, 6 Aug 2026 09:20:21 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 373B66B0088; Thu, 6 Aug 2026 09:20:21 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 23EFC6B008A; Thu, 6 Aug 2026 09:20:21 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0016.hostedemail.com [216.40.44.16]) by kanga.kvack.org (Postfix) with ESMTP id E63A76B007B for ; Thu, 6 Aug 2026 09:20:20 -0400 (EDT) Received: from smtpin07.hostedemail.com (lb01a-stub [10.200.18.249]) by unirelay08.hostedemail.com (Postfix) with ESMTP id 668C1140671 for ; Thu, 6 Aug 2026 13:20:20 +0000 (UTC) X-FDA: 85070903400.07.8D2A441 Received: from mail-pf1-f198.google.com (mail-pf1-f198.google.com [209.85.210.198]) by imf26.hostedemail.com (Postfix) with ESMTP id A1A2714000C for ; Thu, 6 Aug 2026 13:20:18 +0000 (UTC) Authentication-Results: imf26.hostedemail.com; dkim=pass header.d=google.com header.s=20251104 header.b=Rvte7yVo; spf=pass (imf26.hostedemail.com: domain of 3EIp0agYKCFEBxt62vz77z4x.v75416DG-553Etv3.7Az@flex--seanjc.bounces.google.com designates 209.85.210.198 as permitted sender) smtp.mailfrom=3EIp0agYKCFEBxt62vz77z4x.v75416DG-553Etv3.7Az@flex--seanjc.bounces.google.com; dmarc=pass (policy=reject) header.from=google.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1786022418; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=quMxwgvzS8F8CxQzPIpHc+hBSqfVyEO+f6ARjKTQRm8=; b=6AnOk1Bny3rDR/IYteLlJo2b9HxYKIQm838wnrc8mFGv8HqiOyKdvf9X1jER8kolCLBD3Y yavSfRxh3Nio1WJazukglekkbHBhG5OrafPN+fvJxvuP6kPyAxTTBFleOQhE5be/mnC2I4 x9hrdawUIvb7f7JovoQdJiI+ZMC+++A= ARC-Authentication-Results: i=1; imf26.hostedemail.com; dkim=pass header.d=google.com header.s=20251104 header.b=Rvte7yVo; spf=pass (imf26.hostedemail.com: domain of 3EIp0agYKCFEBxt62vz77z4x.v75416DG-553Etv3.7Az@flex--seanjc.bounces.google.com designates 209.85.210.198 as permitted sender) smtp.mailfrom=3EIp0agYKCFEBxt62vz77z4x.v75416DG-553Etv3.7Az@flex--seanjc.bounces.google.com; dmarc=pass (policy=reject) header.from=google.com ARC-Seal: i=1; a=rsa-sha256; d=hostedemail.com; s=arc-20220608; cv=none; t=1786022418; b=ytlLumqspVlPxPW4sREjvzfI4MUmQxkDAPTFiQz/pwzyaf5fURX80LGZqkfzitE2bxuGdN FVxRu0wIqS9AMLE1DdIP1uRg2sdEEV98TOl6woZkDreP1LD5BgOyHunI4U1uHwSzeNiibk KsIcpx4VnGj84rpjdNeVcd6lrMCCB88= Received: by mail-pf1-f198.google.com with SMTP id d2e1a72fcca58-8487eb67173so3592568b3a.2 for ; Thu, 06 Aug 2026 06:20:18 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20251104; t=1786022417; x=1786627217; darn=kvack.org; h=content-type:cc:to:from:subject:message-id:references:mime-version :in-reply-to:date:from:to:cc:subject:date:message-id:reply-to :content-type; bh=quMxwgvzS8F8CxQzPIpHc+hBSqfVyEO+f6ARjKTQRm8=; b=Rvte7yVo99QmzB4OXvXXlyrm+sowoudcRoihDkQS2EYqwnB47Zf91Xe9KyeUQJ0DJu 9z7Lmo+HYcYXm4DRNZdZAJyWS9frr/sFct9kbM2KLG9MAHn7fVhlqbbAeKcsVabUGkgb /1UszdGNYgAiUEHycaBzXXOkF7747H1OF2w8QBK6T/vunNU1aHPc3cgNtEp/Ze9L7GAq JcIAHXwnSvzJ/wCY7V23t7+a5lpt103HZ8tv0+ZUJx+Dkutf1XieOpXzgN7P9tOrgwcv UtgzQ+SY+c/VgGNW2ojN3gPeKjCuCT0sKSeR3QgkqfERSnckoiptShhj4heiS4V9e2nC RfJw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1786022417; x=1786627217; h=content-type:cc:to:from:subject:message-id:references:mime-version :in-reply-to:date:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to:content-type; bh=quMxwgvzS8F8CxQzPIpHc+hBSqfVyEO+f6ARjKTQRm8=; b=lo6v0qOuN+hxueDV24gvFpxYA67aigcC29b0rfaBvUqymV2pdqadmQ6brAjFAwmDGa vWa3aJqkx3lqrNxCDzkaIRV6VwcXuuvGE1PzHHZT7NMtwS6zG76dCgNXPlpU8LHp2Cf4 ecvfcSIt8CcC+OgO2q/i7UFhv4ASb+uUy7Wd6zemzsmE50ek+XnZAQGP/ryrWraSw2GZ 4fSCE5XXBOKS9t0X+Gkf9XgAG9wKI715nRTR6yTXkG7me3K5cKpCyL29DyBOdLad6v7g te84sQ62P2Bu7E/KaNEnw3PzlfeC6ZdRAniA4CcBHrYtwvdBNsY4HiM1XKotIG11W7Xr KuMg== X-Forwarded-Encrypted: i=1; AHgh+Rpu7go9lUhOgREe3dlmFN38PzEUxXSlx23cGJNRpsKh/Ja5gX/94IXTNCVb3YNBSNM3ZNX8OPnfsA==@kvack.org X-Gm-Message-State: AOJu0Yw/3eHFT8CIKTP87ACDWd1CYHenrH9MHoNWGvkPieH4/g/ie5Ih op93jMBNRT+waXo2Mt9tVj/MUXgcvI0gi4WkEVyGhUWU/9q/V+T6QAgLqf6J9i6Ly9FHWJrlia2 E2C35uw== X-Received: from pfbcj19.prod.google.com ([2002:a05:6a00:2993:b0:84c:3651:a4b1]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a05:6a00:3ccd:b0:845:c7f1:29fa with SMTP id d2e1a72fcca58-84f2e04a63bmr16001363b3a.30.1786022416699; Thu, 06 Aug 2026 06:20:16 -0700 (PDT) Date: Thu, 6 Aug 2026 06:19:45 -0700 In-Reply-To: Mime-Version: 1.0 References: <20260728-gmem-inplace-conversion-v9-0-35f9aec2aed2@google.com> <20260728-gmem-inplace-conversion-v9-3-35f9aec2aed2@google.com> <7dafaa90-f3d4-4be4-a5cc-472163f18040@intel.com> Message-ID: Subject: Re: [PATCH v9 03/41] KVM: Enumerate support for PRIVATE memory iff kvm_arch_has_private_mem is defined From: Sean Christopherson To: Xiaoyao Li Cc: Ackerley Tng , aik@amd.com, andrew.jones@linux.dev, binbin.wu@linux.intel.com, brauner@kernel.org, chao.p.peng@linux.intel.com, david@kernel.org, jmattson@google.com, jthoughton@google.com, michael.roth@amd.com, oupton@kernel.org, pankaj.gupta@amd.com, qperret@google.com, rick.p.edgecombe@intel.com, rientjes@google.com, shivankg@amd.com, steven.price@arm.com, tabba@google.com, willy@infradead.org, wyihan@google.com, yan.y.zhao@intel.com, forkloop@google.com, pratyush@kernel.org, suzuki.poulose@arm.com, aneesh.kumar@kernel.org, liam@infradead.org, Paolo Bonzini , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "H. Peter Anvin" , Steven Rostedt , Masami Hiramatsu , Mathieu Desnoyers , Jonathan Corbet , Shuah Khan , Shuah Khan , Vishal Annapurve , Andrew Morton , Chris Li , Kairui Song , Kemeng Shi , Nhat Pham , Barry Song , Axel Rasmussen , Yuanchu Xie , Wei Xu , Youngjun Park , Qi Zheng , Shakeel Butt , Kiryl Shutsemau , Baoquan He , Jason Gunthorpe , John Hubbard , Peter Xu , Vlastimil Babka , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-kselftest@vger.kernel.org, linux-mm@kvack.org, linux-coco@lists.linux.dev Content-Type: text/plain; charset="us-ascii" X-Stat-Signature: kw7c3364nwefn5ms416aguxnsqryjys5 X-Rspamd-Queue-Id: A1A2714000C X-Rspam-User: X-Rspamd-Server: rspam06 X-HE-Tag: 1786022418-219406 X-HE-Meta: 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 OFU/9hjN 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, Aug 06, 2026, Xiaoyao Li wrote: > On 8/6/2026 8:43 AM, Sean Christopherson wrote: > > On Wed, Aug 05, 2026, Xiaoyao Li wrote: > > > On 7/31/2026 4:34 AM, Ackerley Tng wrote: > > > > I think another way to phrase this is that if we don't make this change, > > > > say, on the foo architecture where there's no CoCo and no private mem > > > > support, kvm_supported_mem_attributes() would return true for the !kvm > > > > case, which is over-reporting. > > > > > > Under the condition that the foo architecture enables > > > CONFIG_KVM_VM_MEMORY_ATTRIBUTES. > > > > > > > How about this, replacing the entire changelog paragraph above: > > > > > > > > Explicitly guard reporting support for KVM_MEMORY_ATTRIBUTE_PRIVATE > > > > based on kvm_arch_has_private_mem being #defined. This improves > > > > reporting accuracy by not reporting support for > > > > KVM_MEMORY_ATTRIBUTE_PRIVATE when kvm_supported_mem_attributes() is > > > > called with kvm == NULL. > > > > > > It doesn't help for the case where kvm == NULL, but help for the case where > > > CONFIG_KVM_VM_MEMORY_ATTRIBUTES is defined but kvm_arch_has_private_mem not. > > > > > > sorry for being picky. I think we can say > > > > > > This improves the reporting accuracy by avoiding the case where > > > KVM_MEMORY_ATTRIBUTE_PRIVATE is reported when kvm == null even without > > > kvm_arch_has_private_mem being #defined. > > > > How about this? > > > > Explicitly guard reporting support for KVM_MEMORY_ATTRIBUTE_PRIVATE based > > on kvm_arch_has_private_mem being #defined in anticipation of tracking > > PRIVATE vs. SHARED state per-guest_memfd, not per-VM (to allow in-place > > conversion). > > Sorry, maybe I'm stupid. I still don't understand how to connect it to > tracking PRIVATE vs. SHARED state per-guest_memfd. > > There are two diffs in this patch, and we are talking about the second diff, > right? Yes, the second diff is what provides the desired change in behavior. > If the kvm_supported_mem_attributes() will be used by gmem, I can buy the > justification. But it won't. At least, it won't after this series. It's not about gmem using that API, it's about non-gmem using the API when reporting KVM_CAP_MEMORY_ATTRIBUTES. Without the change, if KVM supports any memory attributes, i.e. if KVM_GENERIC_MEMORY_ATTRIBUTES=y, then the below will *incorrctly* include PRIVATE in the set of memory attributes, because KVM_CAP_MEMORY_ATTRIBUTES reports what memory attributes are supported via the VM-scoped KVM_SET_MEMORY_ATTRIBUTES. #ifdef CONFIG_KVM_GENERIC_MEMORY_ATTRIBUTES case KVM_CAP_MEMORY_ATTRIBUTES: return kvm_supported_mem_attributes(kvm); #endif > > > guest_memfd support for memory attributes is expected to be unconditional > > to avoid yet more macros (all architectures that support guest_memfd are > > expected to use per-gmem attributes at some point), at which point > > enumerating support KVM_MEMORY_ATTRIBUTE_PRIVATE based solely on memory > > attributes being supported by KVM at-large would result in a system-scope > > s/memory attributes/CONFIG_KVM_VM_MEMORY_ATTRIBUTES/ ? No. I mean "memory attributes" as in KVM as a whole entity, i.e. everything linked into kvm.ko (and kvm-{amd,intel}.ko, supports memory attributes. > > check (NULL @kvm) over-reporting support on arm64. > > I think arm64 won't define CONFIG_KVM_VM_MEMORY_ATTRIBUTES? Precisely *because* of this patch. More at the bottom. > So it seems to have nothing to do with arm64. > > It matters for x86. After patch 20, CONFIG_KVM_VM_MEMORY_ATTRIBUTES is > user-configurable. At that time, people can disable > CONFIG_KVM_SW_PROTECTED_VM, CONFIG_KVM_INTEL_TDX and CONFIG_KVM_AMD_SEV, but > enable CONFIG_KVM_VM_MEMORY_ATTRIBUTES on x86. No, they can't. KVM_VM_MEMORY_ATTRIBUTES depends on one of those three being enabled. What am I missing? config KVM_VM_MEMORY_ATTRIBUTES bool "Enable per-VM PRIVATE vs. SHARED attributes (for CoCo VMs)" depends on KVM_SW_PROTECTED_VM || KVM_INTEL_TDX || KVM_AMD_SEV <====== > In this case, kvm_supported_mem_attributes() reports > KVM_MEMORY_ATTRIBUTE_PRIVATE for system-scope query which is totally wrong. I > think this is the case we want to prevent not something won't happen for > arm64? Well, yeah, because of patches like this one. That's the whole point. Without this change, kvm_supports_private_mem() would be reachable if and only if KVM_VM_MEMORY_ATTRIBUTES=y, which would prevent burying that Kconfig in x86 and would prevent arm64 from enabling the PRIVATE memory attribute in guest_memfd.