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

From: Andy Lutomirski <luto@amacapital.net>
To: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@kernel.org>,
	Ard Biesheuvel <ard.biesheuvel@linaro.org>,
	Matt Fleming <matt@codeblueprint.co.uk>,
	Thomas Gleixner <tglx@linutronix.de>,
	"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>, Borislav Petkov <bp@alien8.de>,
	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: Tue, 29 Sep 2015 18:16:19 -0700	[thread overview]
Message-ID: <CALCETrVvwxZN95swaUDG2fkz9brWV3BQkfMDtLJXZkTRpe8nRg@mail.gmail.com> (raw)
In-Reply-To: <560B34EF.8040408@zytor.com>

On Tue, Sep 29, 2015 at 6:03 PM, H. Peter Anvin <hpa@zytor.com> wrote:
> On 09/27/2015 12:06 AM, Ingo Molnar wrote:
>>
>> * Ard Biesheuvel <ard.biesheuvel@linaro.org> wrote:
>>
>>>> If we allocate the EFI runtime as a single virtual memory block then issues
>>>> like rounding between sections does not even come up as a problem: we map the
>>>> original offsets and sizes byte by byte.
>>>
>>> Well, by that reasoning, we should not call SetVirtualAddressMap() in the first
>>> place, and just use the 1:1 mapping UEFI uses natively. This is more than
>>> feasible on arm64, and I actually fought hard against using
>>> SetVirtualAddressMap() at all, but I was overruled by others. I think this is
>>> also trivially possible on X64, since the 1:1 mapping is already active
>>> alongside the VA mapping.
>>
>> 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.
>>
>
> Pro: by far the sanest way to map the UEFI tables.
> Con: doesn't actually work (breaks on several known platforms.)

Can we at least do 1:1 without an offset on arm64?  Given that Linux
seems to be more of a reference on arm64 than Windows is, maybe that
would give everyone something vaguely sane to work with.

--Andy