linux-kernel - Re: [PATCH 1/2] Create UV efi

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Message-ID: <20160517121122.GC21993@codeblueprint.co.uk>
Date:	Tue, 17 May 2016 13:11:22 +0100
From:	Matt Fleming <matt@...eblueprint.co.uk>
To:	Alex Thorlton <athorlton@....com>
Cc:	linux-kernel@...r.kernel.org, Dimitri Sivanich <sivanich@....com>,
	Russ Anderson <rja@....com>, Mike Travis <travis@....com>,
	Borislav Petkov <bp@...e.de>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
	linux-efi@...r.kernel.org, Mark Rutland <mark.rutland@....com>
Subject: Re: [PATCH 1/2] Create UV efi_call macros

On Mon, 16 May, at 05:58:40PM, Alex Thorlton wrote:
> 
> I was simply re-using the efi_call implementation.  Boris suggested that
> I re-write this using the efi_call_virt macro, so I just went with that.
> It all seems to work just fine, so I don't see much reason to stray away
> from that implementation.  That being said, I'm obviously not a huge fun
> of the code duplication across the macros.  I think there's probably a
> way to minimize this, though I haven't quite worked out the best method
> yet (ideas are welcome :)

The reason I'm pressing for details is that we have a related issue
with the EFI thunking code (CONFIG_EFI_MIXED), where the function
pointer we want to call isn't accessible via the EFI System Table, see
efi_thunk().

Well, technically it *is* accessible, you just can't dereference the
services at runtime because the pointers in the tables are not 64-bit.

But the same constraints exist for EFI thunk and UV code; given a
function pointer to execute that isn't in efi.systab, setup the EFI
runtime environment and call a custom ABI function.

I haven't tested this (or thought through all the implications), but
could you look at providing a table (or something) for mapping a
function name to a ptr,func pair, e.g.

	thunk_get_time:	runtime_services32(get_time), efi64_thunk
	thunk_set_time:	runtime_services32(set_time), efi64_thunk
	...
	uv_call_func: efi.uv_systab->function, uv_efi_call_virt

which we could use in arch_efi_call_virt()? That should give us much
less code duplication and hide all this inside arch/x86.