[PATCH 1/2] powerpc/vas: Report proper error for address translation failure

[Bulent Abali]

copied verbatim from P9 DD2 Nest Accelerators Workbook Version 3.2

Table 4-36. CSB Non-zero CC Reported Error Types

CC=5, Error Type: Translation, 
Comment: Unused, defined by RFC02130 (footnote:  DMA controller uses this 
CC internally in translation fault handling. Do not reuse for other 
purposes.)

CC=240 through 251, reserved for future firmware use, 
Comment: Error codes 240 - 255 (0xF0 - 0xF0) are reserved for firmware use 
and are not signalled by the hardware. 
These CCs are written in the CSB by hypervisor to alert the partition to 
error conditions detected by the hypervisor. 
These codes have been used in past processors for this purpose and ought 
not be relocated.





From:   Haren Myneni/Beaverton/IBM
To:     Michael Ellerman <mpe at ellerman.id.au>
Cc:     abali at us.ibm.com, Haren Myneni <haren at linux.ibm.com>, 
linuxppc-dev at lists.ozlabs.org, 
"Linuxppc-dev"<linuxppc-dev-bounces+hbabu=us.ibm.com at lists.ozlabs.org>, 
rzinsly at linux.ibm.com, tulioqm at br.ibm.com, Haren 
Myneni/Beaverton/IBM at IBMUS
Date:   07/09/2020 04:01 PM
Subject:        Re: [EXTERNAL] Re: [PATCH 1/2] powerpc/vas: Report proper 
error for address translation failure




"Linuxppc-dev" <linuxppc-dev-bounces+hbabu=us.ibm.com at lists.ozlabs.org> 
wrote on 07/09/2020 04:22:10 AM:

> From: Michael Ellerman <mpe at ellerman.id.au>
> To: Haren Myneni <haren at linux.ibm.com>
> Cc: tulioqm at br.ibm.com, abali at us.ibm.com, linuxppc-
> dev at lists.ozlabs.org, rzinsly at linux.ibm.com
> Date: 07/09/2020 04:21 AM
> Subject: [EXTERNAL] Re: [PATCH 1/2] powerpc/vas: Report proper error
> for address translation failure
> Sent by: "Linuxppc-dev" <linuxppc-dev-bounces
> +hbabu=us.ibm.com at lists.ozlabs.org>
> 
> Haren Myneni <haren at linux.ibm.com> writes:
> > DMA controller uses CC=5 internally for translation fault handling. So
> > OS should be using CC=250 and should report this error to the user 
space
> > when NX encounters address translation failure on the request buffer.
> 
> That doesn't really explain *why* the OS must use CC=250.
> 
> Is it documented somewhere that 5 is for hardware use, and 250 is for
> software?

Yes, mentioned in Table 4-36. CSB Non-zero CC Reported Error Types (P9 NX 
DD2 work book). Also footnote for CC=5 says "DMA controller uses this CC 
internally in translation fault handling. Do not reuse for other purposes"

I will add documentation reference for CC=250 comment. 

> 
> > This patch defines CSB_CC_ADDRESS_TRANSLATION(250) and updates
> > CSB.CC with this proper error code for user space.
> 
> We still have:
> 
> #define CSB_CC_TRANSLATION   (5)
> 
> And it's very unclear where one or the other should be used.
> 
> Can one or the other get a name that makes the distinction clear.

CSB_CC_TRANSLATION is added in 842 driver (nx-common-powernv.c) when NX is 
introduced (P7+). NX will not see faults on kernel requests (cc=250) and 
even CC=5. 

Table 4-36: 
For CC=5: says Translation
CC=250:    says "Address Translation Fault"

So I can say CRB_CC_ADDRESS_TRANSLATION_FAULT or CRN_CC_TRANSLATION_FAULT. 
This code path (also CRBs) should be generic, so should not use like 
CRB_CC_NX_FAULT. 

Thanks
Haren

> 
> cheers
> 
> 
> > diff --git a/Documentation/powerpc/vas-api.rst b/Documentation/
> powerpc/vas-api.rst
> > index 1217c2f..78627cc 100644
> > --- a/Documentation/powerpc/vas-api.rst
> > +++ b/Documentation/powerpc/vas-api.rst
> > @@ -213,7 +213,7 @@ request buffers are not in memory. The 
> operating system handles the fault by
> >  updating CSB with the following data:
> > 
> >     csb.flags = CSB_V;
> > -   csb.cc = CSB_CC_TRANSLATION;
> > +   csb.cc = CSB_CC_ADDRESS_TRANSLATION;
> >     csb.ce = CSB_CE_TERMINATION;
> >     csb.address = fault_address;
> > 
> > diff --git a/arch/powerpc/include/asm/icswx.h b/arch/powerpc/
> include/asm/icswx.h
> > index 965b1f3..b1c9a57 100644
> > --- a/arch/powerpc/include/asm/icswx.h
> > +++ b/arch/powerpc/include/asm/icswx.h
> > @@ -77,6 +77,8 @@ struct coprocessor_completion_block {
> >  #define CSB_CC_CHAIN      (37)
> >  #define CSB_CC_SEQUENCE      (38)
> >  #define CSB_CC_HW      (39)
> > +/* User space address traslation failure */
> > +#define   CSB_CC_ADDRESS_TRANSLATION   (250)
> > 
> >  #define CSB_SIZE      (0x10)
> >  #define CSB_ALIGN      CSB_SIZE
> > diff --git a/arch/powerpc/platforms/powernv/vas-fault.c b/arch/
> powerpc/platforms/powernv/vas-fault.c
> > index 266a6ca..33e89d4 100644
> > --- a/arch/powerpc/platforms/powernv/vas-fault.c
> > +++ b/arch/powerpc/platforms/powernv/vas-fault.c
> > @@ -79,7 +79,7 @@ static void update_csb(struct vas_window *window,
> >     csb_addr = (void __user *)be64_to_cpu(crb->csb_addr);
> > 
> >     memset(&csb, 0, sizeof(csb));
> > -   csb.cc = CSB_CC_TRANSLATION;
> > +   csb.cc = CSB_CC_ADDRESS_TRANSLATION;
> >     csb.ce = CSB_CE_TERMINATION;
> >     csb.cs = 0;
> >     csb.count = 0;
> > -- 
> > 1.8.3.1
> 




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