On 7/8/26 15:08, Peter Maydell wrote:
On Mon, 3 Aug 2026 at 05:19, Bin Guo <[email protected]> wrote:
pflash_post_load() did not restore the ROMD mode of the memory region.
Although cmd and wcycle are migrated, the destination retains the
default ROMD = true from realize. When the source was in a non-array
mode (e.g. ID read, cmd = 0x90), reads on the destination bypass
pflash_read() via the ROM fast path and return raw storage bytes
instead of the command-specific response.
Derive ROMD from the migrated cmd/wcycle in pflash_post_load.
Resolves: https://gitlab.com/qemu-project/qemu/-/work_items/4042
Cc: [email protected]
Signed-off-by: Bin Guo <[email protected]>
---
hw/block/pflash_cfi01.c | 10 ++++++++++
1 file changed, 10 insertions(+)
diff --git a/hw/block/pflash_cfi01.c b/hw/block/pflash_cfi01.c
index 5b9ddb20b1..a13b91967e 100644
--- a/hw/block/pflash_cfi01.c
+++ b/hw/block/pflash_cfi01.c
@@ -1030,6 +1030,16 @@ static int pflash_post_load(void *opaque, int version_id)
{
PFlashCFI01 *pfl = opaque;
+ /*
+ * ROMD mode is not in the VMState; derive it from the migrated
+ * cmd and wcycle. Only (wcycle == 0, cmd == 0x00) is read-array.
+ */
+ if (pfl->wcycle == 0 && pfl->cmd == 0x00) {
+ memory_region_rom_device_set_romd(&pfl->mem, true);
+ } else {
+ memory_region_rom_device_set_romd(&pfl->mem, false);
+ }
Confirming that this is correct is a bit tricky. It relies on:
* when we set romd mode to true we also set wcycle = 0, cmd = 0
(which we do, in reset and in the mode_read_array code)
* when we set romd mode to false at the top of pflash_write(),
all paths out of that function either go through the mode_read_array
path, or else update pfl->cmd to something non-zero
* nowhere outside pflash_write() udpates cmd or wcycle except
for the "clear them to 0 and set romd mode" places
This is almost but not quite true. In pflash_read(), the default
case for the pfl->cmd switch sets wcycle = 0 cmd = 0 but doesn't
change the romd state. Luckily the "this should never happen"
comment is true -- there's no way to get a pfl->cmd that falls
into the default (except for being deliberately fed a bogus value
via inbound migration).
Queued amending this audit note ^^, thanks.
It might be worth having that pflash_read() code also set the
romd mode when it clears wcycle and cmd, to make the invariant
more clearly preserved.
But this patch is correct, so:
Reviewed-by: Peter Maydell <[email protected]>
thanks
-- PMM
