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[54.240.197.239]) by smtp.gmail.com with ESMTPSA id iz17-20020a05600c555100b003db07420d14sm2065074wmb.39.2023.01.26.09.49.23 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 26 Jan 2023 09:49:23 -0800 (PST) From: Paul Durrant X-Google-Original-From: Paul Durrant Message-ID: <46ea1f4e-2061-d5f8-2b44-5d24a3a3e7ca@xen.org> Date: Thu, 26 Jan 2023 17:49:22 +0000 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:102.0) Gecko/20100101 Thunderbird/102.6.1 Subject: Re: [SeaBIOS PATCH] xen: require Xen info structure at 0x1000 to detect Xen To: David Woodhouse , seabios , xen-devel , qemu-devel References: Content-Language: en-US Organization: Xen Project In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=2a00:1450:4864:20::334; envelope-from=xadimgnik@gmail.com; helo=mail-wm1-x334.google.com X-Spam_score_int: -31 X-Spam_score: -3.2 X-Spam_bar: --- X-Spam_report: (-3.2 / 5.0 requ) BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, FREEMAIL_FROM=0.001, NICE_REPLY_A=-1.15, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: paul@xen.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On 20/01/2023 11:33, David Woodhouse wrote: > From: David Woodhouse > > When running under Xen, hvmloader places a table at 0x1000 with the e820 > information and BIOS tables. If this isn't present, SeaBIOS will > currently panic. > > We now have support for running Xen guests natively in QEMU/KVM, which > boots SeaBIOS directly instead of via hvmloader, and does not provide > the same structure. > > As it happens, this doesn't matter on first boot. because although we > set PlatformRunningOn to PF_QEMU|PF_XEN, reading it back again still > gives zero. Presumably because in true Xen, this is all already RAM. But > in QEMU with a faithfully-emulated PAM config in the host bridge, it's > still in ROM mode at this point so we don't see what we've just written. > > On reboot, however, the region *is* set to RAM mode and we do see the > updated value of PlatformRunningOn, do manage to remember that we've > detected Xen in CPUID, and hit the panic. > > It's not trivial to detect QEMU vs. real Xen at the time xen_preinit() > runs, because it's so early. We can't even make a XENVER_extraversion > hypercall to look for hints, because we haven't set up the hypercall > page (and don't have an allocator to give us a page in which to do so). > > So just make Xen detection contingent on the info structure being > present. If it wasn't, we were going to panic anyway. That leaves us > taking the standard QEMU init path for Xen guests in native QEMU, > which is just fine. > > Untested on actual Xen but ObviouslyCorrect™. Works for me... Tested-by: Paul Durrant > > Signed-off-by: David Woodhouse > --- > src/fw/xen.c | 45 ++++++++++++++++++++++++++++++++------------- > 1 file changed, 32 insertions(+), 13 deletions(-) > Also... Reviewed-by: Paul Durrant