linux-kernel - Re: [PATCH] phys_efi_set_virtual_address

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Message-ID: <20120620120702.GA3983@srcf.ucam.org>
Date:	Wed, 20 Jun 2012 13:07:02 +0100
From:	Matthew Garrett <mjg59@...f.ucam.org>
To:	Robin Holt <holt@....com>
Cc:	linux-kernel@...r.kernel.org,
	"H. Peter Anvin" <hpa@...ux.intel.com>
Subject: Re: [PATCH] phys_efi_set_virtual_address_map needs va, no pa.

On Wed, Jun 20, 2012 at 03:24:57AM -0500, Robin Holt wrote:
> The kernel allocated memmap may end up being beyond the first
> 512GB of memory.  That early range is identity mapped, while the
> remainder of memory is not.  The net result is the memmap allocated by
> efi_enter_virtual_mode will not be accessible via its __pa as is currently
> passed back to EFI.
> 
> Since EFI is going to have to parse the passed in table, I believe the
> EFI documentation is wrong.
> 
> I asked one of our BIOS engineers to look at the Intel reference code
> and he said it was obvious that the address would have to be a virtaully
> accessible address as we are in virtual mode while EFI is handling the
> callback.

No, that's completely wrong. UEFI can't be called in virtual mode until 
*after* SetVirtualAddressMap(). The UEFI spec indicates that all 
physical memory must have an identity mapping at this stage (section 
2.3.4), so if we don't then that's a bug that needs to be fixed.

-- 
Matthew Garrett | mjg59@...f.ucam.org
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