From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from desiato.infradead.org (desiato.infradead.org [90.155.92.199]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 8EC6B1B0434; Fri, 4 Apr 2025 10:27:31 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=90.155.92.199 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1743762453; cv=none; b=Rj04lZcj2RE1AOs7tizh/V2QX+Q6y2eKq9AbYwnJj2ExXtv5/LA2n2jEknMFQPUKKFgbkuTmkPBP6qB37Tz7rn/rDxeEbfOnGEOEYy8bin0PSH0v1f4/mCzIbtE7GGuHPSJHOFnXLIEH3DiqlgpgQ54Rb7n7FWw1QX/3/H3yULE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1743762453; c=relaxed/simple; bh=GHhoif0NPNclWxe/UopaOZZipFquVeMbDiZimiVi+0g=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=JXsCSKXiSvIMDUY7xgjeGWFDiOTLPed9oWiUE23Svfg6fLlXrSg+I6ILNvRB6IRfad3yFCQe2BAsVs9+zd8dqKWqMgP32ytFPnZL+LMyD+kIEmusyU/FyAmyo7kPxs3dmlw1WLxql0SGRFqahTqMvlWNYt/JBCnsNppqAqbTWM4= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org; spf=none smtp.mailfrom=desiato.srs.infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=TMqJDYJP; arc=none smtp.client-ip=90.155.92.199 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=desiato.srs.infradead.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="TMqJDYJP" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=desiato.20200630; h=MIME-Version:Content-Type:References: In-Reply-To:Date:Cc:To:From:Subject:Message-ID:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=GHhoif0NPNclWxe/UopaOZZipFquVeMbDiZimiVi+0g=; b=TMqJDYJPNBrQBQrHiBi4Caw+9d fY5DYEBGCNdJe8AtvJ3T3EVsVpC8RnpO/0kTzXxV0feF5wLw5yFNG9+sspJPYgU8bnLsqEoKA0iSW UaWc4ia4W7rwrSpGS/HmVUTQkNQukgvVcLYWvJidkKp4XnbyarxD9dxqDqa7cizPV3iX274lsKHO4 AR/Fm4up57Cfw0CxXJQdad8GHb1hpv+0TaMd0oPM6FLCyQkjphLsKTe/kR6mNG9/wx78bF7RT1net oOK1uAPna65cf/OkBYoBBhsiCEmVNu0eKQBWYLljCIk6h/BxCSnGMwOiQ78UFHjKlE/wm6PYruCYi rlKHSJuw==; Received: from [193.117.214.244] (helo=u09cd745991455d.ant.amazon.com) by desiato.infradead.org with esmtpsa (Exim 4.98.1 #2 (Red Hat Linux)) id 1u0eGl-00000007O5S-1S06; Fri, 04 Apr 2025 10:27:27 +0000 Message-ID: <0bc5c470964aa38bc65599d579f8b7bf1afa5ab7.camel@infradead.org> Subject: Re: [RFC PATCH 1/3] content: Add VIRTIO_F_SWIOTLB to negotiate use of SWIOTLB bounce buffers From: David Woodhouse To: Zhu Lingshan , virtio-comment@lists.linux.dev Cc: mst@redhat.com, hch@infradead.org, Claire Chang , linux-devicetree , Rob Herring , =?ISO-8859-1?Q?J=F6rg?= Roedel , iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org, graf@amazon.de Date: Fri, 04 Apr 2025 11:27:26 +0100 In-Reply-To: <1fb64766-f945-494c-ba0d-0123cf498ea2@amd.com> References: <20250402112410.2086892-1-dwmw2@infradead.org> <20250402112410.2086892-2-dwmw2@infradead.org> <1966cbf1-a430-480e-a78d-3d6bbcb4ada4@amd.com> <1fb64766-f945-494c-ba0d-0123cf498ea2@amd.com> Content-Type: multipart/signed; micalg="sha-256"; protocol="application/pkcs7-signature"; boundary="=-PYiV8Rh9LHRJbg+nV5wf" User-Agent: Evolution 3.52.3-0ubuntu1 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-SRS-Rewrite: SMTP reverse-path rewritten from by desiato.infradead.org. See http://www.infradead.org/rpr.html --=-PYiV8Rh9LHRJbg+nV5wf Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Thu, 2025-04-03 at 15:31 +0800, Zhu Lingshan wrote: > On 4/3/2025 3:24 PM, David Woodhouse wrote: > > On Thu, 2025-04-03 at 15:13 +0800, Zhu Lingshan wrote: > > > Hello David > > >=20 > > > IMHO, if we need a bounce buffer, why not place it on the host memory= ? > > As explained in the cover letter, this is designed for the case where > > the device *cannot* easily access host memory. >=20 > Do you mean CoCo encrypted memory? If so, what is the difference between > the host memory side bounce buffer and a device memory bounce buffer > to a guest except the transport(DDR or PCI)? The device should be > able to access host memory side bounce buffer. In the CoCo case, yes. As long as it's *known* to be memory which is shared with the hypervisor, and unsuspecting guests won't accidentally use it as general purpose RAM, then pKVM (or whatever) can happily allow Linux and the VMM to access it. That's basically how it works for virtio-mmio, as I just mentioned in a different subthread. The region referenced by `restricted-dma-pool` is in the guest memory address space, and the "platform" is configured to allow DMA *only* there. Doing the same on the PCI transport (referencing an address range in system address space rather than on the device itself) is slightly unnatural, but as I said if we consider it the responsibility of the firmware to *program* that then we could maybe squint and accept it even in the case of physical devices. I'm not sure I like it much though. --=-PYiV8Rh9LHRJbg+nV5wf Content-Type: application/pkcs7-signature; name="smime.p7s" Content-Disposition: attachment; filename="smime.p7s" Content-Transfer-Encoding: base64 MIAGCSqGSIb3DQEHAqCAMIACAQExDzANBglghkgBZQMEAgEFADCABgkqhkiG9w0BBwEAAKCCD9Aw ggSOMIIDdqADAgECAhAOmiw0ECVD4cWj5DqVrT9PMA0GCSqGSIb3DQEBCwUAMGUxCzAJBgNVBAYT AlVTMRUwEwYDVQQKEwxEaWdpQ2VydCBJbmMxGTAXBgNVBAsTEHd3dy5kaWdpY2VydC5jb20xJDAi BgNVBAMTG0RpZ2lDZXJ0IEFzc3VyZWQgSUQgUm9vdCBDQTAeFw0yNDAxMzAwMDAwMDBaFw0zMTEx MDkyMzU5NTlaMEExCzAJBgNVBAYTAkFVMRAwDgYDVQQKEwdWZXJva2V5MSAwHgYDVQQDExdWZXJv a2V5IFNlY3VyZSBFbWFpbCBHMjCCASIwDQYJKoZIhvcNAQEBBQADggEPADCCAQoCggEBAMjvgLKj jfhCFqxYyRiW8g3cNFAvltDbK5AzcOaR7yVzVGadr4YcCVxjKrEJOgi7WEOH8rUgCNB5cTD8N/Et GfZI+LGqSv0YtNa54T9D1AWJy08ZKkWvfGGIXN9UFAPMJ6OLLH/UUEgFa+7KlrEvMUupDFGnnR06 aDJAwtycb8yXtILj+TvfhLFhafxroXrflspavejQkEiHjNjtHnwbZ+o43g0/yxjwnarGI3kgcak7 nnI9/8Lqpq79tLHYwLajotwLiGTB71AGN5xK+tzB+D4eN9lXayrjcszgbOv2ZCgzExQUAIt98mre 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