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

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Message-ID: <87cyiq3px0.fsf@vajain21.in.ibm.com>
Date: Wed, 20 Nov 2024 20:36:51 +0530
From: Vaibhav Jain <vaibhav@...ux.ibm.com>
To: "Ritesh Harjani (IBM)" <ritesh.list@...il.com>,
        Narayana Murty N
 <nnmlinux@...ux.ibm.com>,
        linuxppc-dev@...ts.ozlabs.org, mpe@...erman.id.au,
        linux-kernel@...r.kernel.org
Cc: mahesh@...ux.ibm.com, oohall@...il.com, npiggin@...il.com,
        christophe.leroy@...roup.eu, maddy@...ux.ibm.com, naveen@...nel.org,
        ganeshgr@...ux.ibm.com, sbhat@...ux.ibm.com
Subject: Re: [PATCH] powerpc/pseries/eeh: Fix get PE state translation

Hi Ritesh,

Thanks for looking into this patch. My responses on behalf of Narayana
below:

"Ritesh Harjani (IBM)" <ritesh.list@...il.com> writes:

> Narayana Murty N <nnmlinux@...ux.ibm.com> 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

>
> 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.

>
> [1]: https://lore.kernel.org/all/1402364517-28561-3-git-send-email-gwshan@linux.vnet.ibm.com/
>
> 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.

>
> -ritesh
>
>>
>> Signed-off-by: Narayana Murty N <nnmlinux@...ux.ibm.com>
>> ---
>>  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