Re: [PATCH v1 2/4] OvmfPkg: IommuDxe: Provide support for mapping BusMasterCommonBuffer operation

[Laszlo Ersek <lersek@redhat.com>]

On 08/02/17 01:51, Brijesh Singh wrote:
> On 8/1/17 4:59 PM, Laszlo Ersek wrote:


>> Please implement the free-list idea that I outlined earlier. Unmap()
>> must not call FreePool() on the MAP_INFO structures.
> 
> Sorry it was my bad. I missed implementing that feedback. I will fix it
> in next rev. As you have outlined in previous feedback that Unmap() can
> be called from ExitBootService() hence i will refrain from using
> FreePool() or MemEncryptSev*() functions in this sequence (except when
> freeing the actual bounce buffer).

No, you have to distinguish the C-bit's management and memory releasing.

Unmap must restore the C bit on the bounce buffer, for all of
BusMasterRead, BusMasterWrite, and BusMasterCommonBuffer. This is
required regardless of whether the bounce buffer was allocated
implicitly (for BusMasterRead and BusMasterWrite) or explicitly (for
BusMasterCommonBuffer, in AllocateBuffer()).

Unmap must zero and release the implicitly allocated bounce buffer for
BusMasterRead, BusMasterWrite.

Unmap must neither zero nor release the explicitly allocated buffer for
BusMasterCommonBuffer. For that operation, FreeBuffer() must do both steps.

Unmap must put MAP_INFO back on the internal free list for
BusMasterCommonBuffer. For BusMasterRead and BusMasterWrite, Unmap can
release MAP_INFO with FreePool().

Thanks
Laszlo