[dpdk-dev] [PATCH v2 3/5] bus/pci: use IOVAs check when setting IOVA mode
Burakov, Anatoly
anatoly.burakov at intel.com
Thu Oct 4 17:49:49 CEST 2018
On 04-Oct-18 2:35 PM, Alejandro Lucero wrote:
>
>
> On Wed, Oct 3, 2018 at 1:56 PM Burakov, Anatoly
> <anatoly.burakov at intel.com <mailto:anatoly.burakov at intel.com>> wrote:
>
> On 31-Aug-18 1:50 PM, Alejandro Lucero wrote:
> > Although VT-d emulation currently only supports 39 bits, it could
> > be iovas being within that supported range. This patch allows
> > IOVA mode in such a case.
> >
> > Indeed, memory initialization code can be modified for using lower
> > virtual addresses than those used by the kernel for 64 bits processes
> > by default, and therefore memsegs iovas can use 39 bits or less for
> > most system. And this is likely 100% true for VMs.
> >
> > Signed-off-by: Alejandro Lucero <alejandro.lucero at netronome.com
> <mailto:alejandro.lucero at netronome.com>>
> > ---
> > drivers/bus/pci/linux/pci.c | 15 ++++++++++-----
> > 1 file changed, 10 insertions(+), 5 deletions(-)
> >
> > diff --git a/drivers/bus/pci/linux/pci.c
> b/drivers/bus/pci/linux/pci.c
> > index 04648ac..215dc10 100644
> > --- a/drivers/bus/pci/linux/pci.c
> > +++ b/drivers/bus/pci/linux/pci.c
> > @@ -588,10 +588,11 @@
> > fclose(fp);
> >
> > mgaw = ((vtd_cap_reg & VTD_CAP_MGAW_MASK) >>
> VTD_CAP_MGAW_SHIFT) + 1;
> > - if (mgaw < X86_VA_WIDTH)
> > - return false;
> >
> > - return true;
> > + if (!rte_eal_check_dma_mask(mgaw))
> > + return true;
> > + else
> > + return false;
>
> return rte_eal_check_dma_mask(mgaw) == 0; ?
>
>
> I guess that works and is more elegant.
> Thanks.
>
>
> > }
> > #elif defined(RTE_ARCH_PPC_64)
> > static bool
> > @@ -615,13 +616,17 @@
> > {
> > struct rte_pci_device *dev = NULL;
> > struct rte_pci_driver *drv = NULL;
> > + int iommu_dma_mask_check_done = 0;
> >
> > FOREACH_DRIVER_ON_PCIBUS(drv) {
> > FOREACH_DEVICE_ON_PCIBUS(dev) {
> > if (!rte_pci_match(drv, dev))
> > continue;
> > - if (!pci_one_device_iommu_support_va(dev))
> > - return false;
> > + if (!iommu_dma_mask_check_done) {
> > + if
> (!pci_one_device_iommu_support_va(dev))
> > + return false;
> > + iommu_dma_mask_check_done = 1;
> > + }
> > }
>
> The commit message doesn't explain why are we only checking a single
> device. Indeed, i am not 100% clear as to why, so some explanation in
> the commit message and preferably a comment in code would be more than
> welcome :)
>
>
> Because the pci_one_device_iommu_support_va function does always the
> same whatever the device is used in the call.
So, this code was always wrong and needlessly checked each device when
it could've checked it a single time? OK, that makes it a bit clearer.
Still, needs to be documented in comments/commit message :) The commit
message IMO looks quite irrelevant to what happens in the commit. It
almost feels like this commit should be split in two - first change the
mgaw check, and then fix the PCI bus code to not check needlessly.
--
Thanks,
Anatoly
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