From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-pg1-f197.google.com (mail-pg1-f197.google.com [209.85.215.197]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id C190B37B41B for ; Thu, 6 Aug 2026 00:43:51 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.215.197 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785977033; cv=none; b=M93Up1YAxaHcT4HLPS9cE4GdmZNRooQRcAdr4uDsDjJovvRDoH+Qg997g+GX7rH1LooeOxmbBZO1pFHIieTrT37+4G+atvrAK+dkU/SAc9z/3TMOQIPaiozrsgRQcRpxDKBH0OMaMLCiVH/QBDry306HbVWrygeGGl5unB07RxE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1785977033; c=relaxed/simple; bh=MOBnrAzJHjAXv0busTUd8AQe2wVTRESDC3GYmdGx6Jc=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=pqT4YUaYAtv/wZ85y1YOflWK9x/CJvMnt1rBGL8kODlLApVnCrPXDDO/Z57iCuZ9oyUvHkoZsX7pCOYrOFo1TW63jo6E1m9GIQvxYYYRH1mbk6V2kFS9AlxJacTxFxlbPY6ZcFd0LRyqmcb+2oyzzGQb11RN3YDF7mmkl94JIt0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--seanjc.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=s9W9uVBX; arc=none smtp.client-ip=209.85.215.197 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--seanjc.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="s9W9uVBX" Received: by mail-pg1-f197.google.com with SMTP id 41be03b00d2f7-c9fe4c5eb39so1186885a12.1 for ; Wed, 05 Aug 2026 17:43:51 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20251104; t=1785977031; x=1786581831; darn=vger.kernel.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=GW1XyS3pE1vmBMrFND4uaqlT60WFAOcGNZed7ARn/tI=; b=s9W9uVBXMZADMYL3esIoidDW/3wdqPJ/VWnjeAbH6rJQJRQPL0AggH0/MOCz7FWeoV EGW4WNmQRuMx2WRkobs6JklVdkd+HnuAtR8jtJ4gUbjU23NQXBvQlRiBLlu8KpzKJc1G XUx5jKHagJDb77xXRqa877eee8TI6vhVWvZHj0OBitBkg8QBF3NnBLs+k1wcrnH1WrKL Xba3KfjDaCPDRtpnL5ff33HcpEBLdJPB3hzbvB37BGUJNXddi1+omIEmN9n8Qnw3NCYi L3wzawiNBzx2tbrN/pDuO+IiJRzFiJ5msDIUPSakKdCbGAicfGYnrwjwmfFT+s7HPha/ aMog== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20251104; t=1785977031; x=1786581831; 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=GW1XyS3pE1vmBMrFND4uaqlT60WFAOcGNZed7ARn/tI=; b=WaMNKIxz26GfWQomkMTefk+uHcOAa7ec2VqdWvoZm8fyVLd82ENTkfYfcWphS6wsbi RFRRFi/idIJYBGerc7v60v972IeYaex4FKAUVtg+YQcIOwACHYW4gKDTrP7tYx7tye53 LubpyrU/I9fXlQIKgkXy2Qf+0qrzpzBEfI6Y0kCwy6sjh1YO2/lHWvRRk8coeWRZ7fBa C7B89wGps8c+FEypERDkr5TMNoDLVPNtXMriSyEAozJk1rxECYE4WnUcQeqDq0qRfl89 KdLFel2OkLuvJKGflfsjcSSwwfCiV/nDbrbpOk6VHqXe2ich/vglZGX36yJEafACxQfN LJVg== X-Forwarded-Encrypted: i=1; AHgh+RoELMTAtArbczYHRFkPuAolJLTyZhJq/17qqMGyw/fehJ2Vo5R95xHVQGOigWsOTXUUBVs=@vger.kernel.org X-Gm-Message-State: AOJu0YzJva4G78Wg20A7FI0yD5+5GktMk0SwHEWLsj/SNg3hPuWWr+ag u2A9FO5yTbkfj4iFnjL1oLWazC+i8tlWKClQO8+smvpBX4HcMT4iKuMhUzijFYqnL1C7O9IJTt7 LkuQAoA== X-Received: from pgki21.prod.google.com ([2002:a63:e455:0:b0:c9e:9c6:a85e]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a05:6a21:6112:b0:3b4:e4f6:4f15 with SMTP id adf61e73a8af0-3cb85e9922cmr13235742637.5.1785977030773; Wed, 05 Aug 2026 17:43:50 -0700 (PDT) Date: Wed, 5 Aug 2026 17:43:50 -0700 In-Reply-To: Precedence: bulk X-Mailing-List: kvm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: 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" 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). 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 check (NULL @kvm) over-reporting support on arm64. > > > Give architectures full control over overriding the default definition > > of kvm_arch_has_private_mem() by removing the coupling with > > CONFIG_KVM_VM_MEMORY_ATTRIBUTES. > > > > In a later patch, kvm_arch_has_private_mem() will be defined based on > > whether architectural features are compiled in, and made orthogonal to > > CONFIG_KVM_VM_MEMORY_ATTRIBUTES. >