On Fri, Jan 12, 2024 at 10:47:43AM +0100, Laszlo Ersek wrote:
> On 1/11/24 14:36, Gerd Hoffmann wrote:
> > In some cases (specifically when the flash update region is
> > small but crosses a multiple of P30_MAX_BUFFER_SIZE_IN_BYTES)
> > NorFlashWriteSingleBlock reads only one instead of two
> > P30_MAX_BUFFER_SIZE_IN_BYTES blocks into the shadow buffer.
> >
> > That leads to random crap being written to the second block,
> > which in turn can corrupt both the variable store and the
> > FTW work space.
> >
> > This patch fixes the calculation.
> >
> > Signed-off-by: Gerd Hoffmann <kra...@redhat.com>
> > ---
> > OvmfPkg/VirtNorFlashDxe/VirtNorFlash.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/OvmfPkg/VirtNorFlashDxe/VirtNorFlash.c
> > b/OvmfPkg/VirtNorFlashDxe/VirtNorFlash.c
> > index 1afd60ce66eb..cdc809d75e3d 100644
> > --- a/OvmfPkg/VirtNorFlashDxe/VirtNorFlash.c
> > +++ b/OvmfPkg/VirtNorFlashDxe/VirtNorFlash.c
> > @@ -566,7 +566,7 @@ NorFlashWriteSingleBlock (
> > Instance,
> > Lba,
> > Offset & ~BOUNDARY_OF_32_WORDS,
> > - (*NumBytes | BOUNDARY_OF_32_WORDS) + 1,
> > + (((Offset & BOUNDARY_OF_32_WORDS) + *NumBytes) |
> > BOUNDARY_OF_32_WORDS) + 1,
> > Instance->ShadowBuffer
> > );
> > if (EFI_ERROR (Status)) {
>
> This patch looks like the output of an excellent bug analysis. I'll need
> more time to review this. If you have a ticket with the analysis
> captured (actual numbers, debugging logs, a concrete backtrace / call
> chain triggering the issue, etc), I'd appreciate a reference.
Yea, that was a few days browsing through the flash and Ftw code,
sprinkling in debug logging, learning how all this works. Have a shell
script resetting a VM in a loop with slowly increasing delay, to trigger
the code paths recovering from interrupted flash writes.
Finding 0xaf (aka PcdDebugClearMemoryValue) in not-yet used places of
the ftw log (which should have been 0xff) was the bit of information
which finally made me find the root cause of the flash corruption.
I have some followup patches I'll send out as patch series in a moment,
one of them adds variables here to make the whole logic easier to
understand.
stay tuned & take care,
Gerd
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