linux-kernel - Re: [PATCH 5/8] x86 boot: remap efi systab runtime from phys to virt

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Message-Id: <20080616030629.df7afc7a.pj@sgi.com>
Date:	Mon, 16 Jun 2008 03:06:29 -0500
From:	Paul Jackson <pj@....com>
To:	"Huang, Ying" <ying.huang@...el.com>
Cc:	mingo@...e.hu, tglx@...utronix.de, yhlu.kernel@...il.com,
	steiner@....com, travis@....com, hpa@...or.com,
	linux-kernel@...r.kernel.org, andi@...stfloor.org,
	akpm@...ux-foundation.org
Subject: Re: [PATCH 5/8] x86 boot: remap efi systab runtime from phys to
 virt

Huang wrote:
> >  			efi.systab = (efi_system_table_t *) (unsigned long) systab;
> > +			efi.systab->runtime = __va(efi.systab->runtime);
> >  		}
> >  	}
> 
> Why do you need this?

I need this so that my kernel can callback into EFI runtime services
post-boot.

> This should be done by firmware in
> efi_set_virtual_address_map().

I don't understand this comment.  I don't see any routine named
'efi_set_virtual_address_map()' in the kernel.  I do see virt_*
and phys_* variants of that name; did you mean one of those?

In any case, I don't understand how this could "be done by firmware."
It is the kernel that is mapping in the firmware somehow to support EFI
runtime services.

> And this doesn't work on i386, because
> runtime code/data area may be not in identity map area (that is > 768M).

Ok ... what code should we add for i386?  Would it be code like I see
above in this efi_enter_virtual_mode() routine:

                if (PFN_UP(end) <= max_pfn_mapped)
                        va = __va(md->phys_addr);
                else
                        va = efi_ioremap(md->phys_addr, size);

I could write similar code for remapping efi.systab->runtime, but
I could not test such code -- could you assist me in that?

-- 
                  I won't rest till it's the best ...
                  Programmer, Linux Scalability
                  Paul Jackson <pj@....com> 1.940.382.4214
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