Re: [dpdk-dev] [PATCH v2] pci_vfio: Support 64KB kernel page_size with vfio-pci driver

["Tone Zhang (Arm Technology China)" <Tone.Zhang@arm.com>]

Hi Anatoly,

I have some comments.

> -----Original Message-----
> From: Tone Zhang (Arm Technology China)
> Sent: Thursday, November 15, 2018 8:49 AM
> To: Burakov, Anatoly <anatoly.burakov@intel.com>; dev@dpdk.org
> Cc: Gavin Hu (Arm Technology China) <Gavin.Hu@arm.com>; Honnappa
> Nagarahalli <Honnappa.Nagarahalli@arm.com>; Steve Capper
> <Steve.Capper@arm.com>; nd <nd@arm.com>
> Subject: RE: [PATCH v2] pci_vfio: Support 64KB kernel page_size with vfio-pci
> driver
> 
> Hi Anatoly,
> 
> Sorry for the late response.
> 
> > -----Original Message-----
> > From: Burakov, Anatoly <anatoly.burakov@intel.com>
> > Sent: Friday, November 9, 2018 8:15 PM
> > To: Tone Zhang (Arm Technology China) <Tone.Zhang@arm.com>;
> > dev@dpdk.org
> > Cc: Gavin Hu (Arm Technology China) <Gavin.Hu@arm.com>; Honnappa
> > Nagarahalli <Honnappa.Nagarahalli@arm.com>; Steve Capper
> > <Steve.Capper@arm.com>; nd <nd@arm.com>
> > Subject: Re: [PATCH v2] pci_vfio: Support 64KB kernel page_size with
> > vfio-pci driver
> >
> > On 09-Nov-18 5:57 AM, tone.zhang wrote:
> > > With a larger PAGE_SIZE it is possible for the MSI table to very
> > > close to the end of the BAR s.t. when we align the start and end of
> > > the MSI table to the PAGE_SIZE, the end offset of the MSI table is
> > > out of the PCI BAR boundary.
> > >
> > > This patch addresses the issue by comparing both the start and the
> > > end offset of the MSI table with the BAR size, and skip the mapping
> > > if it is out of Bar scope.
> > >
> > > The patch fixes the debug log as below:
> > > EAL: Skipping BAR0
> > >
> > > Signed-off-by: tone.zhang <tone.zhang@arm.com>
> > > Reviewed-by: Gavin Hu <Gavin.Hu@arm.com>
> > > Reviewed-by: Honnappa Nagarahalli <honnappa.nagarahalli@arm.com>
> > > Reviewed-by: Steve Capper <Steve.Capper@arm.com>
> > > Reviewed-by: Burakov Anatoly <anatoly.burakov@intel.com>
> >
> > In the future, please don't include my Reviewed tag unless i actually
> > sent one :)
> 
> Thanks a lot! Will keep in mind. 😊
> 
> >
> > > ---
> > >   drivers/bus/pci/linux/pci_vfio.c | 36
> > > +++++++++++++++++++++++++++++++---
> > --
> > >   1 file changed, 31 insertions(+), 5 deletions(-)
> > >
> > > diff --git a/drivers/bus/pci/linux/pci_vfio.c
> > > b/drivers/bus/pci/linux/pci_vfio.c
> > > index 305cc06..9a0affe 100644
> > > --- a/drivers/bus/pci/linux/pci_vfio.c
> > > +++ b/drivers/bus/pci/linux/pci_vfio.c
> > > @@ -445,9 +445,11 @@ pci_vfio_mmap_bar(int vfio_dev_fd, struct
> > mapped_pci_resource *vfio_res,
> > >   	struct pci_msix_table *msix_table = &vfio_res->msix_table;
> > >   	struct pci_map *bar = &vfio_res->maps[bar_index];
> > >
> > > -	if (bar->size == 0)
> > > +	if (bar->size == 0) {
> > >   		/* Skip this BAR */
> > > +		RTE_LOG(INFO, EAL, "Skipping BAR%d\n", bar_index);
> > >   		return 0;
> > > +	}
> > >
> > >   	if (msix_table->bar_index == bar_index) {
> > >   		/*
> > > @@ -456,8 +458,22 @@ pci_vfio_mmap_bar(int vfio_dev_fd, struct
> > mapped_pci_resource *vfio_res,
> > >   		 */
> > >   		uint32_t table_start = msix_table->offset;
> > >   		uint32_t table_end = table_start + msix_table->size;
> > > -		table_end = (table_end + ~PAGE_MASK) & PAGE_MASK;
> > > -		table_start &= PAGE_MASK;
> > > +		table_end = RTE_ALIGN(table_end, PAGE_SIZE);
> > > +		table_start = RTE_ALIGN(table_start, PAGE_SIZE);
> > > +		/* after rounding to PAGE_SIZE, it is over the bar->size,
> > > +		 * fall back to the MSI-X table offset in the bar and
> > > +		 * align with PAGE_SIZE.
> > > +		 */
> >
> > Minor nitpick - wording of comment could be better, for example:
> >
> > if page-aligned start of MSI-X table is beyond BAR size, shrink the
> > mapping size to MSI-X table start address.
> >
> > Also, probably needs newline before comment.
> >
> 
> Will update the code in next version. Thanks!
> 
> > > +		if (table_start >= bar->size) {
> > > +			table_start = RTE_ALIGN_FLOOR(msix_table->offset,
> > > +							PAGE_SIZE);
> > > +			/* after aligning with PAGE_SIZE, if it is less than
> > > +			 * the MSI-X table offset, continue falling back to
> > > +			 * the actual MSI-X table offset in the bar.
> > > +			 */
> >
> > Same here, wording could probably be improved. Suggested rewording:
> >
> > If MSI-X table address, floor-aligned by page size, is lower than
> > actual MSI-X table offset, fall back to using MSI-X table offset as table start.
> >
> > Now that i think of it, this could really be expressed like this:
> >
> > uint32_t aligned = RTE_ALIGN_FLOOR(msix_table->offset, PAGE_SIZE);
> > table_start = RTE_MAX(aligned, msix_table_offset);
> >
> > I believe this would be much clearer.
> >
> 
> Will update the patch.
> 

When enter the judgement, it implies the "msix_table->offset" is NOT page size aligned, I think we can replace the code in the judgement with one line: table_start = msix_table->offset;
It looks more simple. What's your opinion? Thanks!

> > > +			if (table_start < msix_table->offset)
> > > +				table_start = msix_table->offset;
> > > +		}
> > >
> > >   		if (table_start == 0 && table_end >= bar->size) {
> > >   			/* Cannot map this BAR */
> > > @@ -469,8 +485,18 @@ pci_vfio_mmap_bar(int vfio_dev_fd, struct
> > > mapped_pci_resource *vfio_res,
> > >
> > >   		memreg[0].offset = bar->offset;
> > >   		memreg[0].size = table_start;
> > > -		memreg[1].offset = bar->offset + table_end;
> > > -		memreg[1].size = bar->size - table_end;
> > > +		if (bar->size < table_end) {
> > > +			/*
> > > +			 * after rounding to PAGE_SIZE we don't have any space
> > > +			 * left after the MSI table, so don't try and map it.
> > > +			 */
> >
> > Suggested rewording:
> >
> > If MSI-X table end is beyond BAR end, don't attempt to perform second
> mapping.
> >
> 
> Thanks a lot. Will update.
> 
> > > +			memreg[1].offset = 0;
> > > +			memreg[1].size = 0;
> > > +		}
> > > +		else {
> > > +			memreg[1].offset = bar->offset + table_end;
> > > +			memreg[1].size = bar->size - table_end;
> > > +		}
> > >
> > >   		RTE_LOG(DEBUG, EAL,
> > >   			"Trying to map BAR%d that contains the MSI-X "
> > >
> >
> > However, the patch can go in as is if needed, so
> >
> > Reviewed-by: Anatoly Burakov <anatoly.burakov@intel.com>
> >
> 
> Thanks! 😉
> 
> > --
> > Thanks,
> > Anatoly
> 
> Br,
> Tone

Br,
Tone