Re: [PATCH v3 3/3] pci: ROM preallocation for incoming migration

[Vladimir Sementsov-Ogievskiy]

On 19.05.23 08:34, Michael S. Tsirkin wrote:

On Mon, May 15, 2023 at 03:52:29PM +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, like this:

     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

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 <m...@redhat.com>
Signed-off-by: Vladimir Sementsov-Ogievskiy <vsement...@yandex-team.ru>
Reviewed-by: David Hildenbrand <da...@redhat.com>
Reviewed-by: Juan Quintela <quint...@redhat.com>

Breaks build here:

In function ‘pci_add_option_rom’,
     inlined from ‘pci_qdev_realize’ at ../hw/pci/pci.c:2155:5:
../hw/pci/pci.c:2395:13: error: ‘size’ may be used uninitialized 
[-Werror=maybe-uninitialized]
  2395 |         if (load_image_size(path, ptr, size) < 0) {
       |             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
../hw/pci/pci.c: In function ‘pci_qdev_realize’:
../hw/pci/pci.c:2312:13: note: ‘size’ was declared here
  2312 |     int64_t size;
       |             ^~~~

Hmm, but works for me. Anyway that's obviously false-positive, if we are here, 
size is initialized in previous block if (load_file || ..).

So, may be add simply this:

diff --git a/hw/pci/pci.c b/hw/pci/pci.c
index 0f0c83c02f..075c998284 100644
--- a/hw/pci/pci.c
+++ b/hw/pci/pci.c
@@ -2307,7 +2307,7 @@ static void pci_patch_ids(PCIDevice *pdev, uint8_t *ptr, 
uint32_t size)
 static void pci_add_option_rom(PCIDevice *pdev, bool is_default_rom,
                                Error **errp)
 {
-    int64_t size;
+    int64_t size = 0;  /* fix "uninitialized" false-positive */
     g_autofree char *path = NULL;
     char name[32];
     const VMStateDescription *vmsd;

---
  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 3a0107758c..0f0c83c02f 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"
@@ -2308,10 +2309,16 @@ 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 || !strlen(pdev->romfile)) {
          return;
      }
@@ -2341,32 +2348,35 @@ 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));

@@ -2377,15 +2387,18 @@ 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);
+        }
      }

pci_register_bar(pdev, PCI_ROM_SLOT, 0, &pdev->rom);

--
2.34.1

--
Best regards,
Vladimir