Re: [PULL 03/38] pflash: Only read non-zero parts of backend image

[Kevin Wolf]

Am 03.03.2023 um 23:51 hat Maciej S. Szmigiero geschrieben:
> On 8.02.2023 12:19, Cédric Le Goater wrote:
> > On 2/7/23 13:48, Kevin Wolf wrote:
> > > Am 07.02.2023 um 10:19 hat Cédric Le Goater geschrieben:
> > > > On 2/7/23 09:38, Kevin Wolf wrote:
> > > > > Am 06.02.2023 um 16:54 hat Cédric Le Goater geschrieben:
> > > > > > On 1/20/23 13:25, Kevin Wolf wrote:
> > > > > > > From: Xiang Zheng <zhengxiang9@huawei.com>
> > > > > > > 
> > > > > > > Currently we fill the VIRT_FLASH memory space with two 64MB NOR 
> > > > > > > images
> > > > > > > when using persistent UEFI variables on virt board. Actually we 
> > > > > > > only use
> > > > > > > a very small(non-zero) part of the memory while the rest 
> > > > > > > significant
> > > > > > > large(zero) part of memory is wasted.
> > > > > > > 
> > > > > > > So this patch checks the block status and only writes the 
> > > > > > > non-zero part
> > > > > > > into memory. This requires pflash devices to use sparse files for
> > > > > > > backends.
> > > > > > > 
> > > > > > > Signed-off-by: Xiang Zheng <zhengxiang9@huawei.com>
> > > > > > > 
> > > > > > > [ kraxel: rebased to latest master ]
> > > > > > > 
> > > > > > > Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
> > > > > > > Message-Id: <20221220084246.1984871-1-kraxel@redhat.com>
> > > > > > > Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
> > > > > > > Reviewed-by: Kevin Wolf <kwolf@redhat.com>
> > > > > > > Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> > > > > > 
> > > > > > This newly merged patch introduces a "regression" when booting an 
> > > > > > Aspeed
> > > > > > machine. The following extra m25p80 patch (not yet merged) is 
> > > > > > required
> > > > > > for the issue to show:
> > > > > > 
> > > > > >     
> > > > > > https://lore.kernel.org/qemu-devel/20221115151000.2080833-1-clg@kaod.org/
> > > > > > 
> > > > > > U-Boot fails to find the filesystem in that case.
> > > > > > 
> > > > > > It can be easily reproduced with the witherspoon-bmc machine and 
> > > > > > seems
> > > > > > to be related to the use of a UBI filesystem. Other Aspeed machines 
> > > > > > not
> > > > > > using UBI are not impacted.
> > > > > > 
> > > > > > Here is a tentative fix. I don't know enough the block layer to 
> > > > > > explain
> > > > > > what is happening :/
> > > > > 
> > > > > I was puzzled for a moment, but...
> > > > > 
> > > > > > @@ -39,7 +39,7 @@ static int blk_pread_nonzeroes(BlockBack
> > > > > >                return ret;
> > > > > >            }
> > > > > >            if (!(ret & BDRV_BLOCK_ZERO)) {
> > > > > > -            ret = bdrv_pread(bs->file, offset, bytes,
> > > > > 
> > > > > 'bs->file' rather than 'bs' really looks wrong. I think replacing that
> > > > > would already fix the bug you're seeing.
> > > > > 
> > > > > Just to be sure, how did you configure the block backend? bs->file 
> > > > > would
> > > > > happen to work more or less with raw over file-posix (which is 
> > > > > probably
> > > > > what Gerd tested), but I think it breaks with anything else.
> > > > 
> > > > The command is  :
> > > > 
> > > >    $ qemu-system-arm -M witherspoon-bmc -net user \
> > > >     -drive file=/path/to/file.mtd,format=raw,if=mtd \
> > > >     -nographic -serial mon:stdio -snapshot
> > > > 
> > > > If I remove '-snapshot', all works fine.
> > > 
> > > Ok, that makes sense then. -snapshot creates a temporary qcow2 overlay,
> > > and then what your guest sees with bs->file is not the virtual disk
> > > content of the qcow2 image, but the qcow2 file itself.
> > 
> > yes. Same symptom with pflash devices, TCG and KVM. The guest hangs with 
> > -snapshot.
> > 
> > C.
> > 
> > qemu-system-aarch64 -M virt -smp 2 -cpu max -accel tcg,thread=multi 
> > -nographic -m 2G -drive 
> > if=pflash,format=raw,file=/usr/share/edk2/aarch64/QEMU_EFI-silent-pflash.raw,readonly=on
> >  -drive if=pflash,format=raw,file=rhel9-varstore.img -device 
> > virtio-net,netdev=net0,bus=pcie.0,addr=0x3 -netdev user,id=net0 -drive 
> > file=rhel9-arm64.qcow2,if=none,id=disk,format=qcow2,cache=none -device 
> > virtio-blk-device,drive=disk -serial mon:stdio -snapshot
> > 
> > 
> > 
> 
> +1 here for QEMU + KVM/x86: OVMF CODE file fails to load (is all zeroes)
> with either "-snapshot" QEMU command line option or even with just 
> "snapshot=on"
> setting enabled on pflash0.
> 
> Reverting this patch seems to fix the issue.

Hm, so we know the fix, but nobody has submitted it as an actual patch?
I'll send one...

Kevin