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

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Date:	Mon, 16 Jun 2008 16:27:08 +0800
From:	"Huang, Ying" <ying.huang@...el.com>
To:	Paul Jackson <pj@....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

On Mon, 2008-06-16 at 03:06 -0500, Paul Jackson wrote:
> 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?

I mean the EFI runtime service SetVirtualAddressMap() in spec.

> 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.

This should be done in firmware. That is, the EFI system table:
efi.systab and runtime services table: efi.systab->runtime) will be
updated in SetVirtualAddressMap() by firmware. This is specified in
UEFI2.1 spec: Unified Extensible Firmware Interface Specification,
section 7.4 Virtual Memory Services. If the firmware does not do that
for you, please report bug to firmware vendor.

Your patch makes Linux kernel doesn't work on machine with proper
firmware, because the effect is like __va(__va(phys_ptr)).

Best Regards,
Huang Ying

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