Re: Stack issue after warm UEFI reset and MMU enabling on an Armv8 platform

[Vladimir Olovyannikov <vladimir.olovyannikov@broadcom.com>]

On Wed, Sep 19, 2018 at 5:21 PM Bill Paul <wpaul@windriver.com> wrote:
>
> Of all the gin joints in all the towns in all the world, Vladimir
> Olovyannikov
> had to walk into mine at 16:58 on Wednesday 19 September 2018 and say:
>
> > >From: Ard Biesheuvel [mailto:ard.biesheuvel@linaro.org]
> > >Sent: Wednesday, September 19, 2018 4:38 PM
> > >To: Vladimir Olovyannikov
> > >Cc: edk2-devel@lists.01.org
> > >Subject: Re: Stack issue after warm UEFI reset and MMU enabling on an
> > >Armv8 platform
> > >
> > >
> > >On 19 September 2018 at 15:55, Vladimir Olovyannikov
> > >
> > ><vladimir.olovyannikov@broadcom.com> wrote:
> > >>Hi All,
> > >>
> > >>I need UEFI experts help on the problem with Armv8 board on warm UEFI
> > >>reset.
> > >>Cold reset works fine.
> > >>
> > >>Here is how I set up a warm reset:
> > >>
> > >>STATIC
> > >>EFI_STATUS
> > >>ShutdownUefiBootServices (
> > >>
> > >>  VOID
> > >>  )
> > >>
> > >>{
> > >>
> > >>  EFI_STATUS              Status;
> > >>  UINTN                   MemoryMapSize;
> > >>  EFI_MEMORY_DESCRIPTOR   *MemoryMap;
> > >>  UINTN                   MapKey;
> > >>  UINTN                   DescriptorSize;
> > >>  UINT32                  DescriptorVersion;
> > >>  UINTN                   Pages;
> > >>
> > >>  MemoryMap = NULL;
> > >>  MemoryMapSize = 0;
> > >>  Pages = 0;
> > >>
> > >>  do {
> > >>
> > >>    Status = gBS->GetMemoryMap (
> > >>
> > >>                    &MemoryMapSize,
> > >>                    MemoryMap,
> > >>                    &MapKey,
> > >>                    &DescriptorSize,
> > >>                    &DescriptorVersion
> > >>                    );
> > >>
> > >>    if (Status == EFI_BUFFER_TOO_SMALL) {
> > >>
> > >>      Pages = EFI_SIZE_TO_PAGES (MemoryMapSize) + 1;
> > >>      MemoryMap = AllocatePages (Pages);
> > >>
> > >>      //
> > >>      // Get System MemoryMap
> > >>      //
> > >>      Status = gBS->GetMemoryMap (
> > >>
> > >>                      &MemoryMapSize,
> > >>                      MemoryMap,
> > >>                      &MapKey,
> > >>                      &DescriptorSize,
> > >>                      &DescriptorVersion
> > >>                      );
> > >>
> > >>    }
> > >>
> > >>    // Don't do anything between the GetMemoryMap() and
> > >>    ExitBootServices() if (!EFI_ERROR(Status)) {
> > >>
> > >>      Status = gBS->ExitBootServices (gImageHandle, MapKey);
> > >>      if (EFI_ERROR(Status)) {
> > >>
> > >>        FreePages (MemoryMap, Pages);
> > >>        MemoryMap = NULL;
> > >>        MemoryMapSize = 0;
> > >>
> > >>      }
> > >>
> > >>    }
> > >>
> > >>  } while (EFI_ERROR(Status));
> > >>
> > >>  return Status;
> > >>
> > >>}
> > >>
> > >>Then perform
> > >>ArmCleanDataCache ();
> > >>ArmInvalidateDataCache ();
> > >>ArmDisableInstructionCache ();
> > >>ArmInvalidateInstructionCache ();
> > >
> > >These don't do anything useful on ARM. You can only reliably perform
> > >cache
> > >maintenance by virtual address.
> >
> > So, should I just remove them altogether?
> >
> > >>ArmDisableMmu ();
> > >
> > >... so after this call returns, all bets are off with regards to
> > >whether
> > >what is popped from the stack is actually what we pushed when we
> > >entered
> > >the function.
> >
> > OK, thank you for explanation.
> > But this call returns back into ResetLib implementation as it should,
> > and
> > then there is a direct jump to the start of FV.
> > Am I doing anything wrong here?
> > Then, up to the point of enabling of MMU the stack is OK. But right
> > after
> > enabling MMU it points at _ModuleEntryPoint end of function in
> > DxeCoreEntryPoint.c
> > Am I missing anything? Maybe some stack cleanup before jumping to the
> > start
> > of FV?
>
> When the MMU is enabled, does the mapping for the stack pages change? That
> is,
> could the stack now be mapped to different physical page now?
Thanks for ideas Bill,
No, the mapping stays the same.
The issue is only with warm reset, and only on an A72 board.
There is another platform on A53 sharing the same code, which has no issues
with warm reset.
I cannot explain why.
>
> Instead of showing a stack trace, can you dump the stack pages and compare
> the
> before and after contents?
I can clearly see that before and after contents are different.
>
> Assuming the same physical memory pages are still being used, then there
> could
> be a cache flushing problem. What could happen is:
>
> - some stack memory has been touched recently and is now in the data cache
> - changes are made, which are written to the cache, but not yet flushed
> out to
> RAM
> - enabling the MMU causes a full invalidate of the cache
>
> Now when you look at the stack, you see the earlier contents that were in
> RAM
> -- the changes previously only written to the cache have been lost.
>
> Enabling/disabling caches and MMU is always tricky. I can't say for sure,
> but
> I wouldn't be surprised if there's some subtle bug that causes a flush
> operation to be missed and things may just work by coincidence in the cold
> start case.
I might be missing something preparing for warm reset.
Disabling interrupts does not help though.
Ard, I switched off all DMA-capable devices, so am just booting into UEFI
with no disks or network,
disabled interrupts. The issue is here. Any ideas on how to debug it and
fix?
>
> -Bill
>
> > >>Then jump to start of FV:
> > >>
> > >>typedef
> > >>VOID
> > >>
> > >> (EFIAPI *START_FV)(
> > >>
> > >>  VOID
> > >>
> > >>);
> > >>StartOfFv = (START_FV)(UINTN)PcdGet64(PcdFvBaseAddress);
> > >>StartOfFv ();
> > >>
> > >>Now this is what happens on warm reset:
> > >>reset -c warm
> > >>1. Until ArmEnableMmu() gets called, everything works as expected.
> > >>
> > >>    Here is the stack right before ArmEnableMmu() is called:
> > >>     ArmConfigureMmu+0x4f8
> > >>     InitMmu+0x24
> > >>     MemoryPeim+0x440
> > >>     PrePiMain+0x114
> > >>     PrimaryMain+0x68
> > >>     CEntryPoint+0xC4
> > >>     EL2:0x00000000800008BC
> > >>     -----  End of stack info -----
> > >>
> > >>2. Here is the stack as soon as Mmu is enabled with ArmEnableMmu() :
> > >>    ArmConfigureMmu+0x4fc <-- This one is correct, at line 745 in
> > >>
> > >> ArmConfigureMmu() in ArmPkg/Library/ArmMmuLib/AArch64/ArmMmuLibCore.c
> > >> (return EFI_SUCCESS)
> > >>
> > >>   _ModuleEntryPoint+0x24 <-- Wrong. This points directly to
> > >>
> > >> ASSERT(FALSE); and to CpuDeadLoop() in DxeCoreEntryPoint.c, lines
> > >> 59-60.
> > >>
> > >>   El2:0x000000008E5E8300 <-- Absolutely bogus
> > >>
> > >>    --- End of stack info ---
> > >>
> > >>So, as soon as ArmEnableMmu() exits, execution jumps directly to
> > >>CpuDeadLoop() in DxeCoreEntryPoint of _ModuleEntryPoint().
> > >>
> > >>Would be grateful for any advice.
> > >>
> > >>Thank you,
> > >>Vladimir
> >
> > _______________________________________________
> > edk2-devel mailing list
> > edk2-devel@lists.01.org
> > https://lists.01.org/mailman/listinfo/edk2-devel
> --
> =============================================================================
> -Bill Paul            (510) 749-2329 | Senior Member of Technical Staff,
>                  wpaul@windriver.com | Master of Unix-Fu - Wind River
> Systems
> =============================================================================
>    "I put a dollar in a change machine. Nothing changed." - George Carlin
> =============================================================================