Re: [Xen-devel] [PATCH v2 11/19] xen/arm32: Use alternative to skip the check of pending serrors

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Thu, 30 Mar 2017, Julien Grall wrote:
> Hi Wei,
> 
> On 30/03/17 10:13, Wei Chen wrote:
> > We have provided an option to administrator to determine how to
> > handle the SErrors. In order to skip the check of pending SError,
> > in conventional way, we have to read the option every time before
> > we try to check the pending SError. This will add overhead to check
> > the option at every trap.
> > 
> > The ARM32 supports the alternative patching feature. We can use an
> > ALTERNATIVE to avoid checking option at every trap. We added a new
> > cpufeature named "SKIP_CHECK_PENDING_VSERROR". This feature will be
> > enabled when the option is not diverse.
> > 
> > Signed-off-by: Wei Chen <Wei.Chen@xxxxxxx>
> 
> Reviewed-by: Julien Grall <julien.grall@xxxxxxx>
> 
> > ---
> 
> Stefano, this is requiring the alternative patch (see [1]) which is still in
> review.
> 
> Wei, a general rule is to mention the dependencies between series. So we don't
> apply by mistake in the wrong order.

Right. Thanks Wei for sending both the other patch and this series
together, that helps me avoiding mistakes.

But please add a note about the dependencies, just in case I forget.


> Cheers,
> 
> [1] https://lists.xenproject.org/archives/html/xen-devel/2017-03/msg04132.html
> 
> >  xen/arch/arm/arm32/entry.S | 10 ++++++++++
> >  1 file changed, 10 insertions(+)
> > 
> > diff --git a/xen/arch/arm/arm32/entry.S b/xen/arch/arm/arm32/entry.S
> > index 2187226..105cae8 100644
> > --- a/xen/arch/arm/arm32/entry.S
> > +++ b/xen/arch/arm/arm32/entry.S
> > @@ -1,5 +1,6 @@
> >  #include <asm/asm_defns.h>
> >  #include <asm/regs.h>
> > +#include <asm/alternative.h>
> >  #include <public/xen.h>
> > 
> >  #define SAVE_ONE_BANKED(reg)    mrs r11, reg; str r11, [sp, #UREGS_##reg]
> > @@ -44,6 +45,14 @@ save_guest_regs:
> >          SAVE_BANKED(fiq)
> >          SAVE_ONE_BANKED(R8_fiq); SAVE_ONE_BANKED(R9_fiq);
> > SAVE_ONE_BANKED(R10_fiq)
> >          SAVE_ONE_BANKED(R11_fiq); SAVE_ONE_BANKED(R12_fiq);
> > +
> > +        /*
> > +         * If the SKIP_CHECK_PENDING_VSERROR has been set in the cpu
> > feature,
> > +         * the checking of pending SErrors will be skipped.
> > +         */
> > +        ALTERNATIVE("nop",
> > +                    "b skip_check",
> > +                    SKIP_CHECK_PENDING_VSERROR)
> >          /*
> >           * Start to check pending virtual abort in the gap of Guest -> HYP
> >           * world switch.
> > @@ -99,6 +108,7 @@ abort_guest_exit_end:
> >           */
> >          bne return_from_trap
> > 
> > +skip_check:
> >          mov pc, lr
> > 
> >  #define DEFINE_TRAP_ENTRY(trap)                                         \
> > 
> 
> -- 
> Julien Grall
> 

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