Re: [PATCH] powerpc/pseries/eeh: Fix get PE state translation

[Narayana Murty N]

On 22/11/24 1:26 AM, Ritesh Harjani (IBM) wrote:
> Vaibhav Jain <vaibhav@xxxxxxxxxxxxx> writes:
>
> > Hi Ritesh,
> >
> > Thanks for looking into this patch. My responses on behalf of Narayana
> > below:
> >
> > "Ritesh Harjani (IBM)" <ritesh.list@xxxxxxxxx> writes:
> >
> > > Narayana Murty N <nnmlinux@xxxxxxxxxxxxx> writes:
> > >
> > > > The PE Reset State "0" obtained from RTAS calls
> > > > ibm_read_slot_reset_[state|state2] indicates that
> > > > the Reset is deactivated and the PE is not in the MMIO
> > > > Stopped or DMA Stopped state.
> > > >
> > > > With PE Reset State "0", the MMIO and DMA is allowed for
> > > > the PE.
> > > Looking at the PAPR spec - I do agree that it states the same. i.e.
> > > The "0" Initial PE state means the "Not Reset", "Load/Store allowed" &
> > > "DMA allowed" (Normal Operations).
> > >
> > > > The function pseries_eeh_get_state() is currently
> > > > not indicating that to the caller because of  which the
> > > > drivers are unable to resume the MMIO and DMA activity.
> > > It's new to me, but could you help explain the user visible effect
> > > of what gets broken. Since this looks like pseries_eeh_get_state() has
> > > always been like this when it got first implemented.
> > > Is there also a unit test somewhere which you are testing?
> > Without this patch a userspace process performing VFIO EEH-Recovery wont
> > get the correct indication that EEH recovery is completed. Test code at
> > [2] has an example test case that uses VFIO to inject an EEH error on to
> > a pci-device and then waits on it to reach 'EEH_PE_STATE_NORMAL' state
> > . That state is never reached without this patch.
> >
> > [2] :
> > https://github.com/nnmwebmin/vfio-ppc-tests/commit/006d8fdc41a4
> Right. Thanks for helping with that test code. It's much clearer now. So
> after the error inject and/or the PE hot reset, the PE is never reaching
> it's normal state. That is due to this kernel bug in the pseries EEH
> handling, where it fails to advertise the MMIO & DMA enabled capability
> flag back to the caller. This therefore can cause the userspace VFIO
> driver to incorrectly assume that MMIO/DMA operations cannot be done.
>
> > > IIUC eeh_pe_get_state() was implemented[1] for supporting EEH for VFIO PCI
> > > devices. i.e. the VFIO_EEH_PE_GET_STATE operation of VFIO EEH PE ioctl op
> > > uses pseries_eeh_get_state() helper to query PE state on pseries LPAR.
> > > So are you suggesting that EEH functionality for VFIO PCI device was
> > > never enabled/tested before on pseries?
> > VFIO-EEH had been broken for pseries for a quite some time and was
> > recently fixed in kernel. So this issue was probably not discovered
> > until recently when we started testing with userspace VFIO.
> ohk right, then maybe we might have started testing it after the eeh
> error inject op was implemented for pseries here [1].
>
> [1]: https://lore.kernel.org/linuxppc-dev/20240909140220.529333-1-nnmlinux@xxxxxxxxxxxxx/#t
>
> > > [1]: https://lore.kernel.org/all/1402364517-28561-3-git-send-email-gwshan@xxxxxxxxxxxxxxxxxx/
> > >
> > > Checking the powernv side of implementation I do see that it does
> > > enables the EEH_STATE_[MMIO|DMA]_ENABLED flags in the result mask for
> > > the callers. So doing the same for pseries eeh get state implementation
> > > does look like the right thing to do here IMO.
> > >
> > > > The patch fixes that by reflecting what is actually allowed.
> > > You say this is "fixes" so I am also assuming you are also looking for
> > > stable backports of this? If yes - could you please also add the "Fixes"
> > > tag and cc stable?
> > Yes, agree will re-send adding the fixes tag.
> Yes and maybe let's also add some more context & information to the
> commit message from this discussion.
>
> -ritesh
yes Ritesh, added fixes tag and send it to the stable branch also.
> > > -ritesh
> > >
> > > > Signed-off-by: Narayana Murty N <nnmlinux@xxxxxxxxxxxxx>
> > > > ---
> > > >   arch/powerpc/platforms/pseries/eeh_pseries.c | 6 ++++--
> > > >   1 file changed, 4 insertions(+), 2 deletions(-)
> > > >
> > > > diff --git a/arch/powerpc/platforms/pseries/eeh_pseries.c b/arch/powerpc/platforms/pseries/eeh_pseries.c
> > > > index 1893f66371fa..b12ef382fec7 100644
> > > > --- a/arch/powerpc/platforms/pseries/eeh_pseries.c
> > > > +++ b/arch/powerpc/platforms/pseries/eeh_pseries.c
> > > > @@ -580,8 +580,10 @@ static int pseries_eeh_get_state(struct eeh_pe *pe, int *delay)
> > > >   
> > > >   	switch(rets[0]) {
> > > >   	case 0:
> > > > -		result = EEH_STATE_MMIO_ACTIVE |
> > > > -			 EEH_STATE_DMA_ACTIVE;
> > > > +		result = EEH_STATE_MMIO_ACTIVE	|
> > > > +			 EEH_STATE_DMA_ACTIVE	|
> > > > +			 EEH_STATE_MMIO_ENABLED	|
> > > > +			 EEH_STATE_DMA_ENABLED;
> > > >   		break;
> > > >   	case 1:
> > > >   		result = EEH_STATE_RESET_ACTIVE |
> > > > --
> > > > 2.45.2
> > --
> > Cheers
> > ~ Vaibhav

Thank you Ritesh and Vaibhav for reviewing the patch. Please find the

changes addressed in 
https://lore.kernel.org/all/20241212075044.10563-1-nnmlinux@xxxxxxxxxxxxx/.

Regards,

Narayana Murty N