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Date: Thu, 14 Sep 2017 16:08:14 +0800
From: Baoquan He <bhe@redhat.com>
To: Dave Young <dyoung@redhat.com>
Cc: linux-kernel@vger.kernel.org, x86@kernel.org, mingo@redhat.com,
        tglx@linutronix.de, hpa@zytor.com, thgarnie@google.com,
        keescook@chromium.org, akpm@linux-foundation.org,
        yamada.masahiro@socionext.com, rja@hpe.com, frank.ramsay@hpe.com
Subject: Re: [PATCH v2 RESEND 1/2] x86/UV: Introduce a helper function to
 check UV system at earlier stage
Message-ID: <20170914080814.GO12824@x1>
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On 09/14/17 at 03:49pm, Dave Young wrote:
> > > diff --git a/arch/x86/include/asm/uv/uv.h b/arch/x86/include/asm/uv/uv.h
> > > index b5a32231abd8..93d7ad8763ba 100644
> > > --- a/arch/x86/include/asm/uv/uv.h
> > > +++ b/arch/x86/include/asm/uv/uv.h
> > > @@ -18,6 +18,11 @@ extern void uv_nmi_init(void);
> > >  extern void uv_system_init(void);
> > >  extern const struct cpumask *uv_flush_tlb_others(const struct cpumask *cpumask,
> > >  						 const struct flush_tlb_info *info);
> > > +#include <linux/efi.h>
> > > +static inline int is_early_uv_system(void)
> > > +{
> > > +	return !((efi.uv_systab == EFI_INVALID_TABLE_ADDR) || !efi.uv_systab);
> > > +}
> 

Thanks for looking into this, Dave!

> 
> Sorry for jumping in late, I have two questions about the patch:
> 
> 1) For efi tables, the only invalid value is EFI_INVALID_TABLE_ADDR, and
> efi struct is initialized as EFI_INVALID_TABLE_ADDR by default so no
> need to check "|| !efi.uv_systab". Do we have any UV firmware specific
> assumption that "0" is also possible to be assigned?

Hmm, in uv_bios_init() it also checks the !efi.uv_systab case. And
EFI_INVALID_TABLE_ADDR checking is earlier, it won't affect the result
if it's EFI_INVALID_TABLE_ADDR. And !efi.uv_systab can make it safer
since it doesn't work either if efi.uv_systab is 0. Mainly it's not
harmful.

Mike, what's your thought? Should I only check the (efi.uv_systab ==
EFI_INVALID_TABLE_ADDR) case?

> 
> 2) It seems adding this function in uv.h for separating this for uv
> system only purpose. But I feel it is better to put it in efi.h instead.

At the beginning I put it in efi.c, later Mike suggested putting it in
asm/uv/uv.h. You can also find the discussion in below link.
https://patchwork.kernel.org/patch/9732787/

Thanks
Baoquan

> 
> uv_systab is already a member of struct efi, it is in efi.h so it is
> natural to check the table exist or not. Then just include efi.h in
> kaslr.c and use the function.
> 
> something like drivers/firmware/efi/esrt.c: esrt_table_exists()
> 
> Anyway I have no strong opinon, it looks more natural to me though.
> 
> > >  
> > >  #else	/* X86_UV */
> > >  
> > > @@ -30,6 +35,7 @@ static inline const struct cpumask *
> > >  uv_flush_tlb_others(const struct cpumask *cpumask,
> > >  		    const struct flush_tlb_info *info)
> > >  { return cpumask; }
> > > +static inline int is_early_uv_system(void)	{ return 0; }
> > >  
> > >  #endif	/* X86_UV */
> > >  
> > > -- 
> > > 2.5.5
> > > 
> 
> Thanks
> Dave