[PATCH] powerpc: Ignore DSI error caused by the copy/paste instruction

[Haren Myneni]

On Thu, 2022-09-22 at 09:04 +0000, Christophe Leroy wrote:
> 
> Le 22/09/2022 à 10:29, Haren Myneni a écrit :
> > DSI error will be generated when the paste operation is issued on
> > the suspended NX window due to NX state changes. The hypervisor
> > expects the partition to ignore this error during page pault
> > handling. To differentiate DSI caused by an actual HW configuration
> > or by the NX window, a new “ibm,pi-features” type value is defined.
> > Byte 0, bit 3 of pi-attribute-specifier-type is now defined to
> > indicate this DSI error.
> 
> What is NX ? No eXec ? That's what it is usually. But in that case
> it 
> would be the ISI, not DSI.

NX is nest accelerator supports several functions such as compression,
encryption and etc. It is DSI error mentioned in PAPR ("DSI Caused by
User Mode NX")

> 
> > This patch adds changes to read ibm,pi-features property and ignore
> > DSI error in the page fault handling if CPU_FTR_NX_DSI if defined.
> > 
> > Signed-off-by: Haren Myneni <haren at linux.ibm.com>
> > ---
> >   arch/powerpc/include/asm/cputable.h |  5 ++--
> >   arch/powerpc/kernel/prom.c          | 36 +++++++++++++++++++++---
> > -----
> >   arch/powerpc/mm/fault.c             | 17 +++++++++++++-
> >   3 files changed, 45 insertions(+), 13 deletions(-)
> > 
> > diff --git a/arch/powerpc/mm/fault.c b/arch/powerpc/mm/fault.c
> > index 014005428687..154cc1e85770 100644
> > --- a/arch/powerpc/mm/fault.c
> > +++ b/arch/powerpc/mm/fault.c
> > @@ -367,7 +367,22 @@ static void sanity_check_fault(bool is_write,
> > bool is_user,
> >   #elif defined(CONFIG_PPC_8xx)
> >   #define page_fault_is_bad(__err)	((__err) & DSISR_NOEXEC_OR_G)
> >   #elif defined(CONFIG_PPC64)
> > -#define page_fault_is_bad(__err)	((__err) & DSISR_BAD_FAULT_64S)
> > +static inline int page_fault_is_bad(unsigned long __err)
> 
> The name was __err because it was a macro and there was a risk of 
> collision with a 'err' variable in the caller.
> 
> But as it is now a function, you can just call it 'err'.
> 
> And no need of the 'inline' keyword, GCC will inline it anyway.

Thanks for your comments. I will repost the patch with these changes.

> 
> > +{
> > +	unsigned long flag = DSISR_BAD_FAULT_64S;
> > +
> > +	/*
> > +	 * PAPR 14.15.3.4.1
> > +	 * If byte 0, bit 3 of pi-attribute-specifier-type in
> > +	 * ibm,pi-features property is defined, ignore the DSI error
> > +	 * which is caused by the paste instruction on the
> > +	 * suspended NX window.
> > +	 */
> > +	if (cpu_has_feature(CPU_FTR_NX_DSI))
> > +		flag &= ~DSISR_BAD_COPYPASTE;
> > +
> > +	return ((__err) & flag);
> 
> The () around __err was because it was a macro parameter. It is 
> pointless now. And same for the overall ones. Now it can be :
> 
> 	return err & flags;
> 
> > +}
> >   #else
> >   #define page_fault_is_bad(__err)	((__err) & DSISR_BAD_FAULT_32S)
> >   #endif