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Tsirkin" To: Vladimir Sementsov-Ogievskiy Cc: qemu-devel@nongnu.org, marcel.apfelbaum@gmail.com, philmd@linaro.org, david@redhat.com, peterx@redhat.com, pbonzini@redhat.com, den-plotnikov@yandex-team.ru, lersek@redhat.com, kraxel@redhat.com, dgilbert@redhat.com, quintela@redhat.com, armbru@redhat.com Subject: Re: [PATCH v2 3/3] pci: ROM preallocation for incoming migration Message-ID: <20230426002135-mutt-send-email-mst@kernel.org> References: <20230425161434.173022-1-vsementsov@yandex-team.ru> <20230425161434.173022-4-vsementsov@yandex-team.ru> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20230425161434.173022-4-vsementsov@yandex-team.ru> Received-SPF: pass client-ip=170.10.129.124; envelope-from=mst@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -22 X-Spam_score: -2.3 X-Spam_bar: -- X-Spam_report: (-2.3 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.171, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=-0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 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: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Tue, Apr 25, 2023 at 07:14:34PM +0300, Vladimir Sementsov-Ogievskiy wrote: > On incoming migration we have the following sequence to load option > ROM: > > 1. On device realize we do normal load ROM from the file > > 2. Than, on incoming migration we rewrite ROM from the incoming RAM > block. If sizes mismatch we fail. let's mention an example error message: Size mismatch: 0000:00:03.0/virtio-net-pci.rom: 0x40000 != 0x80000: Invalid argument > > This is not ideal when we migrate to updated distribution: we have to > keep old ROM files in new distribution and be careful around romfile > property to load correct ROM file. > Which is loaded actually just to > allocate the ROM with correct length. > Note, that romsize property doesn't really help: if we try to specify > it when default romfile is larger, it fails with something like: > > romfile "efi-virtio.rom" (160768 bytes) is too large for ROM size 65536 Something I'd like to clarify is that the comment applies to uses where users/distributions supply their own ROM file. And lots of users/distributions seem to have already painted themselves into a corner by supplying a mix of ROM files of unmatching sizes - basically they don't understand the detail of live migration, ROM size interaction with it and with memory layout, etc - as a very small number of people does. For example, ubuntu doubled ROM file size by padding their ROMs with 0xffffffff at some point, breaking migration for all existing machine types. just a web search for Size mismatch: 0000:00:03.0/virtio-net-pci.rom: 0x40000 != 0x80000: Invalid argument will turn up a bunch of confused distros and users. > > Let's just ignore ROM file when romsize is specified and we are in > incoming migration state. In other words, we need only to preallocate > ROM of specified size, local ROM file is unrelated. > > This way: > > If romsize was specified on source, we just use same commandline as on > source, and migration will work independently of local ROM files on > target. > > If romsize was not specified on source (and we have mismatching local > ROM file on target host), we have to specify romsize on target to match > source romsize. romfile parameter may be kept same as on source or may > be dropped, the file is not loaded anyway. > > As a bonus we avoid extra reading from ROM file on target. > > Note: when we don't have romsize parameter on source command line and > need it for target, it may be calculated as aligned up to power of two > size of ROM file on source (if we know, which file is it) or, > alternatively it may be retrieved from source QEMU by QMP qom-get > command, like > > { "execute": "qom-get", > "arguments": { > "path": "/machine/peripheral/CARD_ID/virtio-net-pci.rom[0]", > "property": "size" } } > > Suggested-by: Michael S. Tsirkin > Signed-off-by: Vladimir Sementsov-Ogievskiy > --- > hw/pci/pci.c | 77 ++++++++++++++++++++++++++++++---------------------- > 1 file changed, 45 insertions(+), 32 deletions(-) > > diff --git a/hw/pci/pci.c b/hw/pci/pci.c > index a442f8fce1..e2cab622e4 100644 > --- a/hw/pci/pci.c > +++ b/hw/pci/pci.c > @@ -36,6 +36,7 @@ > #include "migration/vmstate.h" > #include "net/net.h" > #include "sysemu/numa.h" > +#include "sysemu/runstate.h" > #include "sysemu/sysemu.h" > #include "hw/loader.h" > #include "qemu/error-report.h" > @@ -2293,10 +2294,16 @@ static void pci_add_option_rom(PCIDevice *pdev, bool is_default_rom, > { > int64_t size; > g_autofree char *path = NULL; > - void *ptr; > char name[32]; > const VMStateDescription *vmsd; > > + /* > + * In case of incoming migration ROM will come with migration stream, no > + * reason to load the file. Neither we want to fail if local ROM file > + * mismatches with specified romsize. > + */ > + bool load_file = !runstate_check(RUN_STATE_INMIGRATE); > + > if (!pdev->romfile) { > return; > } CC pbonzini,dgilbert,quintela,armbru : guys, is poking at runstate_check like this the right way to figure out we are not going to use the device locally before incoming migration will overwrite ROM contents? > @@ -2329,32 +2336,35 @@ static void pci_add_option_rom(PCIDevice *pdev, bool is_default_rom, > return; > } > > - path = qemu_find_file(QEMU_FILE_TYPE_BIOS, pdev->romfile); > - if (path == NULL) { > - path = g_strdup(pdev->romfile); > - } > + if (load_file || pdev->romsize == -1) { > + path = qemu_find_file(QEMU_FILE_TYPE_BIOS, pdev->romfile); > + if (path == NULL) { > + path = g_strdup(pdev->romfile); > + } > > - size = get_image_size(path); > - if (size < 0) { > - error_setg(errp, "failed to find romfile \"%s\"", pdev->romfile); > - return; > - } else if (size == 0) { > - error_setg(errp, "romfile \"%s\" is empty", pdev->romfile); > - return; > - } else if (size > 2 * GiB) { > - error_setg(errp, "romfile \"%s\" too large (size cannot exceed 2 GiB)", > - pdev->romfile); > - return; > - } > - if (pdev->romsize != -1) { > - if (size > pdev->romsize) { > - error_setg(errp, "romfile \"%s\" (%u bytes) " > - "is too large for ROM size %u", > - pdev->romfile, (uint32_t)size, pdev->romsize); > + size = get_image_size(path); > + if (size < 0) { > + error_setg(errp, "failed to find romfile \"%s\"", pdev->romfile); > + return; > + } else if (size == 0) { > + error_setg(errp, "romfile \"%s\" is empty", pdev->romfile); > + return; > + } else if (size > 2 * GiB) { > + error_setg(errp, > + "romfile \"%s\" too large (size cannot exceed 2 GiB)", > + pdev->romfile); > return; > } > - } else { > - pdev->romsize = pow2ceil(size); > + if (pdev->romsize != -1) { > + if (size > pdev->romsize) { > + error_setg(errp, "romfile \"%s\" (%u bytes) " > + "is too large for ROM size %u", > + pdev->romfile, (uint32_t)size, pdev->romsize); > + return; > + } > + } else { > + pdev->romsize = pow2ceil(size); > + } > } > > vmsd = qdev_get_vmsd(DEVICE(pdev)); > @@ -2365,15 +2375,18 @@ static void pci_add_option_rom(PCIDevice *pdev, bool is_default_rom, > memory_region_init_rom(&pdev->rom, OBJECT(pdev), name, pdev->romsize, > &error_fatal); > > - ptr = memory_region_get_ram_ptr(&pdev->rom); > - if (load_image_size(path, ptr, size) < 0) { > - error_setg(errp, "failed to load romfile \"%s\"", pdev->romfile); > - return; > - } > + if (load_file) { > + void *ptr = memory_region_get_ram_ptr(&pdev->rom); > > - if (is_default_rom) { > - /* Only the default rom images will be patched (if needed). */ > - pci_patch_ids(pdev, ptr, size); > + if (load_image_size(path, ptr, size) < 0) { > + error_setg(errp, "failed to load romfile \"%s\"", pdev->romfile); > + return; > + } > + > + if (is_default_rom) { > + /* Only the default rom images will be patched (if needed). */ > + pci_patch_ids(pdev, ptr, size); > + } > } it kind of feels weird to ignore > pci_register_bar(pdev, PCI_ROM_SLOT, 0, &pdev->rom); > -- > 2.34.1