Re: [PATCH] iommu/amd: Fix event counter availability check

[Paul Menzel]

Dear Alexander,


Thank you very much for the patch.


Am 31.05.20 um 09:22 schrieb Alexander Monakov:

> Adding Shuah Khan to Cc: I've noticed you've seen this issue on Ryzen 2400GE;
> can you have a look at the patch? Would be nice to know if it fixes the
> problem for you too.

> On Fri, 29 May 2020, Alexander Monakov wrote:
>
> > The driver performs an extra check if the IOMMU's capabilities advertise
> > presence of performance counters: it verifies that counters are writable
> > by writing a hard-coded value to a counter and testing that reading that
> > counter gives back the same value.
> >
> > Unfortunately it does so quite early, even before pci_enable_device is
> > called for the IOMMU, i.e. when accessing its MMIO space is not
> > guaranteed to work. On Ryzen 4500U CPU, this actually breaks the test:
> > the driver assumes the counters are not writable, and disables the
> > functionality.
> >
> > Moving init_iommu_perf_ctr just after iommu_flush_all_caches resolves
> > the issue. This is the earliest point in amd_iommu_init_pci where the
> > call succeeds on my laptop.
> >
> > Signed-off-by: Alexander Monakov <amonakov@xxxxxxxxx>
> > Cc: Joerg Roedel <joro@xxxxxxxxxx>
> > Cc: Suravee Suthikulpanit <suravee.suthikulpanit@xxxxxxx>
> > Cc: iommu@xxxxxxxxxxxxxxxxxxxxxxxxxx
> > ---
> >
> > PS. I'm seeing another hiccup with IOMMU probing on my system:
> > pci 0000:00:00.2: can't derive routing for PCI INT A
> > pci 0000:00:00.2: PCI INT A: not connected
> >
> > Hopefully I can figure it out, but I'd appreciate hints.

I guess itâs a firmware bug, but I contacted the linux-pci folks [1].

> >   drivers/iommu/amd_iommu_init.c | 6 +++---
> >   1 file changed, 3 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/iommu/amd_iommu_init.c b/drivers/iommu/amd_iommu_init.c
> > index 5b81fd16f5fa..1b7ec6b6a282 100644
> > --- a/drivers/iommu/amd_iommu_init.c
> > +++ b/drivers/iommu/amd_iommu_init.c
> > @@ -1788,8 +1788,6 @@ static int __init iommu_init_pci(struct amd_iommu *iommu)
> >   	if (iommu->cap & (1UL << IOMMU_CAP_NPCACHE))
> >   		amd_iommu_np_cache = true;
> >   
> > -	init_iommu_perf_ctr(iommu);
> > -
> >   	if (is_rd890_iommu(iommu->dev)) {
> >   		int i, j;
> >   
> > @@ -1891,8 +1889,10 @@ static int __init amd_iommu_init_pci(void)
> >   
> >   	init_device_table_dma();
> >   
> > -	for_each_iommu(iommu)
> > +	for_each_iommu(iommu) {
> >   		iommu_flush_all_caches(iommu);
> > +		init_iommu_perf_ctr(iommu);
> > +	}
> >   
> >   	if (!ret)
> >   		print_iommu_info();
> >
> > base-commit: 75caf310d16cc5e2f851c048cd597f5437013368

Thank you very much for fixing this issue, which is almost two years old 
for me.

Tested-by: Paul Menzel <pmenzel@xxxxxxxxxxxxx>
MSI MSI MS-7A37/B350M MORTAR with AMD Ryzen 3 2200G
Link: https://lore.kernel.org/linux-iommu/20180727102710.GA6738@xxxxxxxxxx/


Kind regards,

Paul


[1]: 
https://lore.kernel.org/linux-pci/8579bd14-e369-1141-917b-204d20cff528@xxxxxxxxxxxxx/