Re: [PATCH 2/2] arm64/efi: Don't pad between EFI_MEMORY_RUNTIME regions

From: Ingo Molnar <mingo@kernel.org>
To: Borislav Petkov <bp@alien8.de>
Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>,
	Matt Fleming <matt@codeblueprint.co.uk>,
	Thomas Gleixner <tglx@linutronix.de>,
	"H. Peter Anvin" <hpa@zytor.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"linux-efi@vger.kernel.org" <linux-efi@vger.kernel.org>,
	Leif Lindholm <leif.lindholm@linaro.org>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Will Deacon <will.deacon@arm.com>,
	"stable@vger.kernel.org" <stable@vger.kernel.org>,
	Matt Fleming <matt.fleming@intel.com>,
	Mark Rutland <mark.rutland@arm.com>,
	Mark Salter <msalter@redhat.com>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Andy Lutomirski <luto@kernel.org>,
	Denys Vlasenko <dvlasenk@redhat.com>,
	Brian Gerst <brgerst@gmail.com>
Subject: Re: [PATCH 2/2] arm64/efi: Don't pad between EFI_MEMORY_RUNTIME regions
Date: Mon, 28 Sep 2015 08:20:15 +0200	[thread overview]
Message-ID: <20150928062015.GB21690@gmail.com> (raw)
In-Reply-To: <20150927104014.GA7631@pd.tnic>

* Borislav Petkov <bp@alien8.de> wrote:

> On Sun, Sep 27, 2015 at 09:06:44AM +0200, Ingo Molnar wrote:
>
> > Could we please re-list all the arguments pro and contra of 1:1 physical 
> > mappings, in a post that also explains the background so that more people can 
> > chime in, not just people versed in EFI internals? It's very much possible 
> > that a bad decision was made.
> 
> The main reason why we did the additional, top-down mapping was kexec kernel 
> wanting to use UEFI runtime facilities too and the braindead design of 
> SetVirtualAddressMap() being callable only once per system boot. So we had to 
> have stable mappings which are valid in the kexec-ed kernel too.
> 
> But this was long time ago and I most certainly have forgotten all the details.
> 
> And now I'm wondering why didn't we do the 1:1 thing and rebuild the exact same 
> EFI pagetable in the kexec-ed kernel? Because when we do an EFI call, we switch 
> to the special pagetable so why didn't we make the kexec-ed kernel rebuild the 
> 1:1 pagetable which it can use for EFI calls...

Yeah.

> Hmm, again, I've forgotten a lot of details so I'm sure Matt will come in and 
> say "No, you can't do that because..."

Would be nice to re-examine all this.

Thanks,

	Ingo