linux-kernel - Re: [PATCHv2 1/5] efi/runtime-wrappers: add {__,}efi_call

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Date:	Thu, 21 Apr 2016 13:55:07 +0100
From:	Mark Rutland <mark.rutland@....com>
To:	Leif Lindholm <leif.lindholm@...aro.org>
Cc:	linux-efi@...r.kernel.org, ard.biesheuvel@...aro.org,
	catalin.marinas@....com, hpa@...or.com, linux@....linux.org.uk,
	matt@...eblueprint.co.uk, mingo@...hat.com, tglx@...utronix.de,
	will.deacon@....com, linux-kernel@...r.kernel.org
Subject: Re: [PATCHv2 1/5] efi/runtime-wrappers: add {__,}efi_call_virt
 templates

On Thu, Apr 21, 2016 at 12:42:56PM +0100, Leif Lindholm wrote:
> On Thu, Apr 21, 2016 at 12:35:25PM +0100, Mark Rutland wrote:
> > Currently each architecture must implement two macros, efi_call_virt and
> > __efi_call_virt, which only differ by the presence or absence of a
> > return type. Otherwise, the logic surrounding the call is identical.
> > 
> > As each architecture must define the entire body of each, we can't place
> > any generic manipulation (e.g. irq flag validation) in the middle.
> > 
> > This patch adds template implementations of these macros. With these,
> > arch code can implement three template macros, avoiding reptition for
> > the void/non-void return cases:
> > 
> > * arch_efi_call_virt_setup
> > 
> >   Sets up the environment for the call (e.g. switching page tables,
> >   allowing kernel-mode use of floating point, if required).
> > 
> > * arch_efi_call_virt
> > 
> >   Performs the call. The last expression in the macro must be the call
> >   itself, allowing the logic to be shared by the void and non-void
> >   cases.
> > 
> > * arch_efi_call_virt_teardown
> > 
> >   Restores the usual kernel environment once the call has returned.
> > 
> > While the savings from repition are minimal, we additionally gain the
> > ability to add common code around the call with the call enviroment set
> > up. This can be used to detect common firmware issues (e.g. bad irq mask
> > management).
> > 
> > Signed-off-by: Mark Rutland <mark.rutland@....com>
> > Cc: Matt Fleming <matt@...eblueprint.co.uk>
> > Cc: linux-efi@...r.kernel.org
> > Cc: linux-kernel@...r.kernel.org
> > ---
> >  drivers/firmware/efi/runtime-wrappers.c | 21 +++++++++++++++++++++
> >  1 file changed, 21 insertions(+)
> > 
> > diff --git a/drivers/firmware/efi/runtime-wrappers.c b/drivers/firmware/efi/runtime-wrappers.c
> > index de69530..1b9fa54 100644
> > --- a/drivers/firmware/efi/runtime-wrappers.c
> > +++ b/drivers/firmware/efi/runtime-wrappers.c
> > @@ -20,6 +20,27 @@
> >  #include <linux/spinlock.h>
> >  #include <asm/efi.h>
> >  
> > +
> > +#ifndef efi_call_virt
> 
> So ... not a strong complaint, but I would prefer if these weren't
> ifdefd. I presume this is because ia64?

Yup, and to allow the gradual migration of arm/arm64/x86 without a new
CONFIG_WANT_GENERIC_EFI_CALL_VIRT or something to that effect.

> Could that be given a dummy pass-through version instead?

I'm not exactly sure what you mean by that. Could you elaborate?

> If not, could a comment be added that this is to retain compatibility
> with ia64 (so that if that architecture was to mysteriously disappear
> from the tree, someone might remember to deconditionalise it)?

Sure. I can also add a note to the commit message regarding the
temporary need while arm/arm64/x86 are moved over.

Thanks,
Mark.

> > +#define efi_call_virt(f, args...)					\
> > +({									\
> > +	efi_status_t __s;						\
> > +	arch_efi_call_virt_setup();					\
> > +	__s = arch_efi_call_virt(f, args);				\
> > +	arch_efi_call_virt_teardown();					\
> > +	__s;								\
> > +})
> > +#endif
> > +
> > +#ifndef __efi_call_virt
> > +#define __efi_call_virt(f, args...)					\
> > +({									\
> > +	arch_efi_call_virt_setup();					\
> > +	arch_efi_call_virt(f, args);					\
> > +	arch_efi_call_virt_teardown();					\
> > +})
> > +#endif
> > +
> >  /*
> >   * According to section 7.1 of the UEFI spec, Runtime Services are not fully
> >   * reentrant, and there are particular combinations of calls that need to be
> > -- 
> > 1.9.1
> > 
>