linux-kernel - Re: [PATCH] Map in physical addresses in efi_map_region

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Date:	Wed, 17 Aug 2016 15:01:51 +0800
From:	Dave Young <dyoung@...hat.com>
To:	Alex Thorlton <athorlton@....com>
Cc:	Borislav Petkov <bp@...en8.de>,
	Matt Fleming <matt@...eblueprint.co.uk>,
	linux-kernel@...r.kernel.org, Russ Anderson <rja@....com>,
	Dimitri Sivanich <sivanich@....com>,
	Mike Travis <travis@....com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
	linux-efi@...r.kernel.org
Subject: Re: [PATCH] Map in physical addresses in efi_map_region_fixed

> > Why do you guys need the physical mapping all of a sudden?
> 
> It's not that we need it all of the sudden, necessarily, it's just that
> we've had to make other changes to make things work with the new,
> (almost) completely isolated, EFI page tables.  We ended up choosing the
> lesser of two evils, and have decided to temporarily rely on the
> physical address of our runtime code, instead of continuing to rely on
> EFI_OLD_MEMMAP.

In efi_map_region, there is already mapped md->phys_addr for broken
firmware. SGI still need EFI_OLD_MEMMAP? I means in 1st kernel instead
of kexec kernel.

void __init efi_map_region(efi_memory_desc_t *md)
{
        unsigned long size = md->num_pages << PAGE_SHIFT;
        u64 pa = md->phys_addr;

        if (efi_enabled(EFI_OLD_MEMMAP))
                return old_map_region(md);

        /*
         * Make sure the 1:1 mappings are present as a catch-all for
         * b0rked
         * firmware which doesn't update all internal pointers after
         * switching
         * to virtual mode and would otherwise crap on us.
         */
        __map_region(md, md->phys_addr);

[snip]

Thanks
Dave