From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: mx.groups.io; dkim=missing; spf=pass (domain: redhat.com, ip: 209.132.183.28, mailfrom: lersek@redhat.com) Received: from mx1.redhat.com (mx1.redhat.com [209.132.183.28]) by groups.io with SMTP; Fri, 20 Sep 2019 02:28:37 -0700 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 6B05E641C7; Fri, 20 Sep 2019 09:28:36 +0000 (UTC) Received: from lacos-laptop-7.usersys.redhat.com (ovpn-120-165.rdu2.redhat.com [10.10.120.165]) by smtp.corp.redhat.com (Postfix) with ESMTP id 83B0F60C80; Fri, 20 Sep 2019 09:28:23 +0000 (UTC) Subject: Re: [edk2-devel] [Qemu-devel] [PATCH 1/2] q35: implement 128K SMRAM at default SMBASE address To: Igor Mammedov Cc: devel@edk2.groups.io, qemu-devel@nongnu.org, yingwen.chen@intel.com, phillip.goerl@oracle.com, alex.williamson@redhat.com, jiewen.yao@intel.com, jun.nakajima@intel.com, michael.d.kinney@intel.com, pbonzini@redhat.com, boris.ostrovsky@oracle.com, rfc@edk2.groups.io, joao.m.martins@oracle.com, Brijesh Singh References: <20190917130708.10281-1-imammedo@redhat.com> <20190917130708.10281-2-imammedo@redhat.com> <561f4440-7c06-10d7-80ce-bbfa810fec59@redhat.com> <20190920102855.3fe2b689@redhat.com> From: "Laszlo Ersek" Message-ID: Date: Fri, 20 Sep 2019 11:28:22 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: <20190920102855.3fe2b689@redhat.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.39]); Fri, 20 Sep 2019 09:28:36 +0000 (UTC) Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit On 09/20/19 10:28, Igor Mammedov wrote: > On Thu, 19 Sep 2019 19:02:07 +0200 > "Laszlo Ersek" wrote: > >> Hi Igor, >> >> (+Brijesh) >> >> long-ish pondering ahead, with a question at the end. > [...] > >> Finally: can you please remind me why we lock down 128KB (32 pages) at >> 0x3_0000, and not just half of that? What do we need the range at >> [0x4_0000..0x4_FFFF] for? > > > If I recall correctly, CPU consumes 64K of save/restore area. > The rest 64K are temporary RAM for using in SMI relocation handler, > if it's possible to get away without it then we can drop it and > lock only 64K required for CPU state. It won't help with SEV > conflict though as it's in the first 64K. OK. Let's go with 128KB for now. Shrinking the area is always easier than growing it. > On QEMU side, we can drop black-hole approach and allocate > dedicated SMRAM region, which explicitly gets mapped into > RAM address space and after SMI hanlder initialization, gets > unmapped (locked). So that SMRAM would be accessible only > from SMM context. That way RAM at 0x30000 could be used as > normal when SMRAM is unmapped. I prefer the black-hole approach, introduced in your current patch series, if it can work. Way less opportunity for confusion. I've started work on the counterpart OVMF patches; I'll report back. Thanks Laszlo