From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-qt1-f175.google.com (mail-qt1-f175.google.com [209.85.160.175]) (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 4F0651D86DC for ; Fri, 27 Feb 2026 00:21:08 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.160.175 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772151669; cv=none; b=llUTYGfDSrVQ/mJX4psgl7f2xMTxKIwT34TV11UQ9P/rjY/pFHrjOdfYpB3VL+lqAZ4xev5oRDBFCbRHksgg5+AAIjkZcHiHZt/nYJUAwHq8CzPtam3W6n0FCDhidGKFRPQSDIKsgKm0D/PpCaqfS9qb6ktKYLvDxIl3PQP6ANU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772151669; c=relaxed/simple; bh=1H1E6m/3SBzjbZermb/QgS4pChpnCVDklOtdppC5Ybw=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=Muq4FgDWORP6iu4mWOj/FdzIyGwSYoEqXV92gX7Xc03AFPeJ5cpjiTDZ3Nr22ohW9IgR3vPq5Jc/J+6UPZXhtkX5n1PTAbtHaqpzPboVIJZsc3spJneIerT53Z0VHTASkj3YACrF9+OE4Syio2ZL/JlIEq9gMg3oWEhJS1gvVvc= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=ziepe.ca; spf=pass smtp.mailfrom=ziepe.ca; dkim=pass (2048-bit key) header.d=ziepe.ca header.i=@ziepe.ca header.b=MmDlufTW; arc=none smtp.client-ip=209.85.160.175 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=ziepe.ca Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=ziepe.ca Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=ziepe.ca header.i=@ziepe.ca header.b="MmDlufTW" Received: by mail-qt1-f175.google.com with SMTP id d75a77b69052e-5069df1de6fso12732451cf.3 for ; Thu, 26 Feb 2026 16:21:08 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ziepe.ca; s=google; t=1772151667; x=1772756467; darn=lists.linux.dev; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:from:to:cc:subject:date:message-id:reply-to; bh=LZJ67b0vcINlAFMObCVMgz4IqYLAlWLPJaI4jITHQUI=; b=MmDlufTWi2F20ECvgWugI7kMiF1wNcaIKDvVb44MyEd5ErTm6Cy3YifXl8bMhERdaY 85LQ3GcjZp8f06ZsG0wU5kaR+vOKVcMKfDu23C8RBpOBdSklqTxLi3TuERWnWlWC8EEK bbDdP5Y2DYo/g4nmQl0IoZlj28B7d/l7+6KOYPjE3ejXjkTKZsE/n2XdyM1YhNSpvwJ/ vyjchWUR9sfVAWbyxnHBRijHjVLQ3ZPqo+rQ+UL2yqOuRoNGJwIUvsX9Nfs2qYWjfr1L Eb7giT8rzTjQ9TToKyqbnbR96kcEmLSZ9I0vxUpFOnqn3iIH4IWA3LeLwztgHrSZ76Fb HVbw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1772151667; x=1772756467; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:x-gm-gg:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=LZJ67b0vcINlAFMObCVMgz4IqYLAlWLPJaI4jITHQUI=; b=oWIt/pFTDoKFCFYzPT1T9zPcR+L2/a+IBcubZF94fnAX4BZ3RqDbKX+wdg04QS+kwj 72gIz9mWKhid5cHy11Al3saO3X/cY/ec+/JipqMEL9DX/YCkRpSgkFZt+4efYUapqXFW wj/aWV/BeLn/zPdVagbyc6xsxlh+cFQjsGCPqXWuHJdAB4RyytGKqvmrWSt1gYFVJXLi BFcnJ8vDB1FCK4hv2ueptOEkmyVCkKEDvxVy72zRMYnO8IkGJJxltn0E11ilCp7htdvt oDrwydrkCcsgGGHz3LwW8Li9/YUKajCVfWJZGmZ/7Jrjf98moXa7bZKhiMckrk+owzl7 aM3Q== X-Forwarded-Encrypted: i=1; AJvYcCWuJYB7HG51OKWZ1V0ayR0j2coepvvD4L8fLqEXAqF1czpgJxAwMHQWp9ovmumppDUttYiNYSH11+it@lists.linux.dev X-Gm-Message-State: AOJu0YyA198+xZ9zv9BascZ2GEUPhwiZchrGZMUVnMMTR6EvxBSBT8C1 lR2febhFU2VO5R0R+BNYqXz5jObW1cgHKRcmgIc1dI5NiSNJhqAvZlOxEYqVM4HSZys= X-Gm-Gg: ATEYQzzuiSsNHd0yPCT7kgWBN19tBtmwJUt9Tr6Y3bpiuwfQm/tlnWQgAJ7nPbwkUw8 lGP6gkPnmh3mAJR+T4jRdbdUSPCqBExxZVtR3xwdpgncnfaZxqMRaOYn0VhrCKQpALUakmfFHNK 0C8w98SOevD30tNLaNEfbFv6oZdXzIKyqTCL5BeLj/cAw045kT13PR9S8MQWuF6AV1UJyI2gFAo +YNR4A89Dp4+SkQBZnAk3dtmXn0bCEN24awWUPH9G068upqZgPWFlm3QFvCA3tnbVqHzsee6MWY +JGDu7wsCv3Jqv2tMzKZ1sowzTUlNRX/9F0rPzf0CPvWFHaRrGTCsshL8JRmEowGNQ244G0Oxhe 0+m3FKiTyDTPnDzRyRmSFkDmwk6Ge4OkQ1UoEnhRkXE0Un2/hxQA+GJjaThjPg/stU8tYf2XbWs qQnWneiwJAk9UeazOjME6b24CW10NDC1OwznS84hPBG6PyM4jKkJvBPHW70xR4qBySEfnT0BF0l ksL7Cr3 X-Received: by 2002:a05:622a:3cb:b0:502:f07e:8569 with SMTP id d75a77b69052e-5075282779dmr12593871cf.35.1772151667151; Thu, 26 Feb 2026 16:21:07 -0800 (PST) Received: from ziepe.ca (hlfxns017vw-142-162-112-119.dhcp-dynamic.fibreop.ns.bellaliant.net. [142.162.112.119]) by smtp.gmail.com with ESMTPSA id d75a77b69052e-50744963095sm36791911cf.3.2026.02.26.16.21.06 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 26 Feb 2026 16:21:06 -0800 (PST) Received: from jgg by wakko with local (Exim 4.97) (envelope-from ) id 1vvlbN-00000000pwc-2290; Thu, 26 Feb 2026 20:21:05 -0400 Date: Thu, 26 Feb 2026 20:21:05 -0400 From: Jason Gunthorpe To: Sean Christopherson Cc: Ackerley Tng , Alexey Kardashevskiy , linux-kernel@vger.kernel.org, kvm@vger.kernel.org, Kevin Tian , Joerg Roedel , Will Deacon , Robin Murphy , Paolo Bonzini , Steve Sistare , Nicolin Chen , iommu@lists.linux.dev, linux-coco@lists.linux.dev, Dan Williams , Santosh Shukla , "Pratik R . Sampat" , Fuad Tabba , Xu Yilun , "Aneesh Kumar K . V" , michael.roth@amd.com, vannapurve@google.com Subject: Re: [RFC PATCH kernel] iommufd: Allow mapping from KVM's guest_memfd Message-ID: <20260227002105.GC44359@ziepe.ca> References: <20260225075211.3353194-1-aik@amd.com> <20260226190757.GA44359@ziepe.ca> Precedence: bulk X-Mailing-List: linux-coco@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Thu, Feb 26, 2026 at 02:40:50PM -0800, Sean Christopherson wrote: > > If guestmemfd is fully pinned and cannot free memory outside of > > truncate that may be good enough (though somehow I think that is not > > the case) > > With in-place conversion, PUNCH_HOLE and private=>shared conversions are the only > two ways to partial "remove" memory from guest_memfd, so it may really be that > simple. PUNCH_HOLE can be treated like truncate right? I'm confused though - I thought in-place conversion ment that private<->shared re-used the existing memory allocation? Why does it "remove" memory? Or perhaps more broadly, where is the shared memory kept/accessed in these guest memfd systems? Jason