Re: [edk2-devel] [PATCH v2] MdeModulePkg/NonDiscoverablePciDeviceDxe: Allow partial FreeBuffer

["Ard Biesheuvel" <ardb@kernel.org>]

On Thu, 8 Sept 2022 at 17:39, Jeff Brasen <jbrasen@nvidia.com> wrote:
>
>
>
> > -----Original Message-----
> > From: Ard Biesheuvel <ardb@kernel.org>
> > Sent: Monday, August 15, 2022 8:42 AM
> > To: devel@edk2.groups.io; Jeff Brasen <jbrasen@nvidia.com>
> > Cc: hao.a.wu@intel.com; ray.ni@intel.com; quic_llindhol@quicinc.com;
> > ardb+tianocore@kernel.org
> > Subject: Re: [edk2-devel] [PATCH v2]
> > MdeModulePkg/NonDiscoverablePciDeviceDxe: Allow partial FreeBuffer
> >
> > External email: Use caution opening links or attachments
> >
> >
> > On Fri, 5 Aug 2022 at 18:56, Jeff Brasen via groups.io
> > <jbrasen=nvidia.com@groups.io> wrote:
> > >
> > >
> > >
> > > > -----Original Message-----
> > > > From: Ard Biesheuvel <ardb@kernel.org>
> > > > Sent: Tuesday, August 2, 2022 10:51 AM
> > > > To: Jeff Brasen <jbrasen@nvidia.com>
> > > > Cc: devel@edk2.groups.io; hao.a.wu@intel.com; ray.ni@intel.com;
> > > > quic_llindhol@quicinc.com; ardb+tianocore@kernel.org
> > > > Subject: Re: [PATCH v2] MdeModulePkg/NonDiscoverablePciDeviceDxe:
> > > > Allow partial FreeBuffer
> > > >
> > > > External email: Use caution opening links or attachments
> > > >
> > > >
> > > > On Tue, 2 Aug 2022 at 17:32, Jeff Brasen <jbrasen@nvidia.com> wrote:
> > > > >
> > > > >
> > > > >
> > > > > > -----Original Message-----
> > > > > > From: Ard Biesheuvel <ardb@kernel.org>
> > > > > > Sent: Friday, July 29, 2022 9:48 AM
> > > > > > To: Jeff Brasen <jbrasen@nvidia.com>
> > > > > > Cc: devel@edk2.groups.io; hao.a.wu@intel.com; ray.ni@intel.com;
> > > > > > quic_llindhol@quicinc.com; ardb+tianocore@kernel.org
> > > > > > Subject: Re: [PATCH v2] MdeModulePkg/NonDiscoverablePciDeviceDxe:
> > > > > > Allow partial FreeBuffer
> > > > > >
> > > > > > External email: Use caution opening links or attachments
> > > > > >
> > > > > >
> > > > > > On Thu, 28 Jul 2022 at 13:25, Jeff Brasen <jbrasen@nvidia.com> wrote:
> > > > > > >
> > > > > > >
> > > > > > > Adding Leif/Ard to CC incase they have any comments on this patch.
> > > > > > >
> > > > > >
> > > > > > This generally looks ok to me. I just wonder if it wouldn't be
> > > > > > simpler to reuse the existing allocation descriptor if it is not
> > > > > > being freed entirely. Given the [presumably] the most common
> > > > > > case is to allocate and then free some pages at the end,
> > > > > > lowering the page count on the existing descriptor would cover
> > > > > > most cases, and we'd only need to allocate new ones if pages are
> > > > > > being freed at the start or in
> > > > the middle.
> > > > >
> > > > > There is often freeing at the beginning as well as this is being
> > > > > used to create
> > > > a 64K aligned section of memory in the case. So it over allocates
> > > > and the free's some at the beginning and the end. I could probably
> > > > make it detect and use that but figured this code would support all
> > > > cases and required less case specific detection.
> > > > >
> > > >
> > > > Ah interesting. Would it help if the allocate routine aligned
> > > > allocations to their size?
> > >
> > > The PciIo->AllocateBuffer function doesn't support passing the request in so
> > we would need to know that info beforehand. The current calling in the XHCI
> > driver does a free at the beginning and then the end of the buffer so we could
> > the existing allocation tracker but figured it would be better to correct the
> > function just in case someone called it to free in the middle.
> > >
> >
> > What I was wondering is whether such allocations are themselves multiples of
> > 64k. This is perhaps orthogonal to the issue this patch addresses, as we'' still
> > need to deal with partial free calls regardless. But I was curious whether XHCI in
> > particular, and perhaps more generally, we could streamline this by aligning all
> > allocations to a log2 upper bound of their sizes.
>
> Xhci code (https://github.com/tianocore/edk2/blob/master/MdeModulePkg/Bus/Pci/XhciDxe/UsbHcMem.c#L604) in allocation requested is greater the EFI_PAGE_SIZE allocates number of requested pages plus pages for the alignment and then frees pages at the beginning and end of the allocation.  I am not sure we really could change this without adding an alignment field to the PciIo protocol.
>
> Is there anything else you would like to change on this patch?
>

No. Thanks for the clarification.

Reviewed-by: Ard Biesheuvel <ardb@kernel.org>