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

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

On Wed, 21 Sept 2022 at 18:27, Jeff Brasen via groups.io
<jbrasen=nvidia.com@groups.io> wrote:
>
> Anything else needed to get this merged?
>

That is up to the MdeModulePkg maintainers.

> > -----Original Message-----
> > From: Ard Biesheuvel <ardb@kernel.org>
> > Sent: Thursday, September 8, 2022 9:55 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: [edk2-devel] [PATCH v2]
> > MdeModulePkg/NonDiscoverablePciDeviceDxe: Allow partial FreeBuffer
> >
> > External email: Use caution opening links or attachments
> >
> >
> > 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/Xhci
> > Dxe/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>
>
>
> 
>
>