Re: [RFC PATCH 1/2] ArmVirtPkg/NorFlashQemuLib: disregard our primary FV

[Laszlo Ersek <lersek@redhat.com>]

On 11/28/18 20:16, Ard Biesheuvel wrote:
> The primary FV contains the firmware boot image, which is not
> runtime updatable in our case. So exposing it to the NOR flash
> driver is undesirable, since it may attempt to modify the NOR
> flash contents.

With you so far.

> It is also rather pointless, since we don't
> keep anything there that we don't already expose via the FVB
> protocol instances that DXE core creates for us based on the
> FV HOBs

I don't follow -- the DXE core does rely on the FV HOBs that we create for it, but I don't remember the DXE core creating FVB protocol instances. An FVB ("firmware volume block") protocol instance is usually created by a flash driver. What am I missing?

Do you mean handles with MemoryMapped(...)/FvFile(...) and Fv(...)/FvFile(...) device paths on them? That point into firmware volumes (that have been supposedly decompressed from flash to RAM)?

> (and so there is nothing the partition or file system
> drivers could potentially attach to via the block I/O and disk
> I/O protocol instances that the NOR flash driver creates)

Ugh, NorFlashDxe creates BlockIo and DiskIo interfaces itself???

Let's see...

/*
  Although DiskIoDxe will automatically install the DiskIO protocol whenever
  we install the BlockIO protocol, its implementation is sub-optimal as it reads
  and writes entire blocks using the BlockIO protocol. In fact we can access
  NOR flash with a finer granularity than that, so we can improve performance
  by directly producing the DiskIO protocol.
*/

Umm... this flash driver does a lot more than I thought it did... or should. :)


Anyway I think it should suffice to say in the commit message that we don't want to expose the first flash device as an FVB protocol instance, because (a) it's read-only, and (b) in the DXE phase, we don't use anything from that flash device. It contains:
- the reset vector,
- the SEC module,
- (for ArmVirtQemu) the non-compressed PEI core, and PEIMs,
- and a compressed bunch of DXE modules (incl. the DXE core) which are decompressed to RAM anyway.
 
> So let's disregard the NOR flash block that covers the primary
> FV.

OK.

> 
> Contributed-under: TianoCore Contribution Agreement 1.1
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> ---
>  ArmVirtPkg/Library/NorFlashQemuLib/NorFlashQemuLib.inf |  5 +++++
>  ArmVirtPkg/Library/NorFlashQemuLib/NorFlashQemuLib.c   | 13 +++++++++++--
>  2 files changed, 16 insertions(+), 2 deletions(-)
> 
> diff --git a/ArmVirtPkg/Library/NorFlashQemuLib/NorFlashQemuLib.inf b/ArmVirtPkg/Library/NorFlashQemuLib/NorFlashQemuLib.inf
> index d86ff36dbd58..c5752a243e6b 100644
> --- a/ArmVirtPkg/Library/NorFlashQemuLib/NorFlashQemuLib.inf
> +++ b/ArmVirtPkg/Library/NorFlashQemuLib/NorFlashQemuLib.inf
> @@ -28,6 +28,7 @@ [Sources.common]
>  [Packages]
>    MdePkg/MdePkg.dec
>    ArmPlatformPkg/ArmPlatformPkg.dec
> +  ArmPkg/ArmPkg.dec
>    ArmVirtPkg/ArmVirtPkg.dec
>  
>  [LibraryClasses]
> @@ -40,3 +41,7 @@ [Protocols]
>  
>  [Depex]
>    gFdtClientProtocolGuid
> +
> +[Pcd]
> +  gArmTokenSpaceGuid.PcdFvBaseAddress
> +  gArmTokenSpaceGuid.PcdFvSize
> diff --git a/ArmVirtPkg/Library/NorFlashQemuLib/NorFlashQemuLib.c b/ArmVirtPkg/Library/NorFlashQemuLib/NorFlashQemuLib.c
> index 2678f57eaaad..72b47bdb5a78 100644
> --- a/ArmVirtPkg/Library/NorFlashQemuLib/NorFlashQemuLib.c
> +++ b/ArmVirtPkg/Library/NorFlashQemuLib/NorFlashQemuLib.c
> @@ -75,13 +75,22 @@ NorFlashPlatformGetDevices (
>        Size = SwapBytes64 (ReadUnaligned64 ((VOID *)&Reg[2]));
>        Reg += 4;
>  
> +      PropSize -= 4 * sizeof (UINT32);
> +
> +      //
> +      // Disregard any flash devices that overlap with the primary FV.
> +      // The firmware is not updatable from inside the guest anyway.
> +      //
> +      if ((PcdGet64 (PcdFvBaseAddress) + PcdGet32 (PcdFvSize) >= Base) &&
> +          (Base + Size) >= PcdGet64 (PcdFvBaseAddress)) {
> +        continue;
> +      }
> +

The overlap condition is expressed correctly, in general, I think; however, both subconditions are off-by-one each. In each, we compare an exclusive limit (one's end) with an inclusive limit (the other's base). And, when exclusive equals inclusive, there is no overlap; they are directly adjacent only. I'd drop the equal signs.


>        mNorFlashDevices[Num].DeviceBaseAddress = (UINTN)Base;
>        mNorFlashDevices[Num].RegionBaseAddress = (UINTN)Base;
>        mNorFlashDevices[Num].Size              = (UINTN)Size;
>        mNorFlashDevices[Num].BlockSize         = QEMU_NOR_BLOCK_SIZE;
>        Num++;
> -
> -      PropSize -= 4 * sizeof (UINT32);
>      }
>    }
>  
> 

Thanks
Laszlo