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

[Laszlo Ersek <lersek@redhat.com>]

On 11/29/18 00:06, Ard Biesheuvel wrote:
> On Wed, 28 Nov 2018 at 23:54, Laszlo Ersek <lersek@redhat.com> wrote:
>>
>> 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)?
>>
> 
> The DXE core dispatcher calls CoreProcessFvImageFile() for all FV
> images it encounters, but looking closer, that only happens for
> embedded FV images, not the primary one.
> 
> But that still means the primary FV contains nothing we actually need.

OK; I missed CoreProcessFvImageFile(). Even though it's specified in
Vol2, "10.4 Firmware Volume Image Files", of the PI-1.6 spec.

Thanks
Laszlo


> 
>>> (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