linux-kernel - Re: [PATCH 1/3] arm64: add EFI stub

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Message-ID: <20131216154601.GH17713@arm.com>
Date:	Mon, 16 Dec 2013 15:46:01 +0000
From:	Catalin Marinas <catalin.marinas@....com>
To:	Mark Salter <msalter@...hat.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"patches@...aro.org" <patches@...aro.org>,
	Ard Biesheuvel <ard.biesheuvel@...aro.org>,
	Will Deacon <Will.Deacon@....com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"matt.fleming@...el.com" <matt.fleming@...el.com>,
	"linux-efi@...r.kernel.org" <linux-efi@...r.kernel.org>,
	Leif Lindholm <leif.lindholm@...aro.org>,
	"roy.franz@...aro.org" <roy.franz@...aro.org>
Subject: Re: [PATCH 1/3] arm64: add EFI stub

On Fri, Dec 06, 2013 at 02:55:54PM +0000, Mark Salter wrote:
> On Thu, 2013-12-05 at 14:18 +0000, Catalin Marinas wrote:
> > On Fri, Nov 29, 2013 at 10:05:10PM +0000, Mark Salter wrote:
> > > +       add     x2, sp, 16
> > > +       str     x8, [x2]
> > > +       bl      efi_entry
> > > +       cmn     x0, #1
> > > +       b.eq    efi_load_fail
> > > +
> > > +       /*
> > > +        * efi_entry() will have relocated the kernel image if necessary
> > > +        * and we return here with device tree address in x0 and the kernel
> > > +        * entry point stored at *image_addr. Save those values in registers
> > > +        * which are preserved by __flush_dcache_all.
> > > +        */
> > > +       ldr     x1, [sp, #16]
> > > +       mov     x20, x0
> > > +       mov     x21, x1
> > > +
> > > +       bl      __flush_dcache_all
> > 
> > Regarding __flush_dcache_all, I plan to remove it for all cases apart
> > from power management with the MMU disabled. With MMU enabled, there is
> > no guarantee that this function does the right thing. It's even worse in
> > the guest context.
> 
> According to booting.txt, the dcache needs to be invalidated. Is there
> something existing I can use or do I need to write it?

The function will stay for a few cases where needed. But here the
D-cache and MMU are still on at this point and there is a slight chance
of speculative loads after the flush (though only clean lines). You
could move this after he MMU disabling (but still keep the I-cache on
for performance).

-- 
Catalin
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