linux-kernel - Re: [PATCH 1/3 -v4] x86_64 EFI runtime service support: EFI basic runtime service support

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Message-Id: <1193361434.23935.226.camel@caritas-dev.intel.com>
Date:	Fri, 26 Oct 2007 09:17:14 +0800
From:	"Huang, Ying" <ying.huang@...el.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	akpm@...ux-foundation.org, "H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, Andi Kleen <ak@...e.de>,
	Chandramouli Narayanan <mouli@...ux.intel.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3 -v4] x86_64 EFI runtime service support: EFI basic
	runtime service support

On Thu, 2007-10-25 at 11:01 -0600, Eric W. Biederman wrote:
> > +static efi_status_t __init phys_efi_set_virtual_address_map(
> > +	unsigned long memory_map_size,
> > +	unsigned long descriptor_size,
> > +	u32 descriptor_version,
> > +	efi_memory_desc_t *virtual_map)
> > +{
> > +	efi_status_t status;
> > +
> > +	efi_call_phys_prelog();
> > +	status = lin2win4((void *)efi_phys.set_virtual_address_map,
> > +			  (u64)memory_map_size, (u64)descriptor_size,
> > +			  (u64)descriptor_version, (u64)virtual_map);
> > +	efi_call_phys_epilog();
> > +	return status;
> > +}
> 
> So you still have this piece of code which makes a kernel using
> efi not compatible with kexec.  But you are still supporting a physical
> call mode for efi.  If you are going to do this can we please just
> remove the hacks that make the EFI physical call mode early boot only
> and just always use that mode.  Depending on weird call once functions
> like efi_set_virtual_address_map makes me very uncomfortable.

The kexec issue is solved as that of IA-64. The EFI runtime code and
data memory area is mapped with identity mapping, so they will have same
virtual address across kexec. The memory mapped IO memory area used by
EFI runtime services is mapped with fixmap, so they will have same
virtual address across kexec too. And the efi_set_virtual_address_map
runtime service function will be skipped in the kexeced kernel (set to
"nop" in /sbin/kexec). So the kexeced kernel can use the virtual mode of
EFI from kernel bootstrap on.

Best Regards,
Huang Ying
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