Message-ID: <4D86F2C2.9080707@redhat.com>
Date:	Mon, 21 Mar 2011 14:40:02 +0800
From:	Cong Wang <amwang@...hat.com>
To:	Matthew Garrett <mjg@...hat.com>
CC:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Vivek Goyal <vgoyal@...hat.com>, linux-kernel@...r.kernel.org,
	Takao Indoh <tindoh@...hat.com>,
	Randy Dunlap <rdunlap@...otime.net>,
	Len Brown <lenb@...nel.org>, linux-doc@...r.kernel.org,
	linux-acpi@...r.kernel.org, "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [Patch] acpi: introduce "acpi_addr=" parameter for kdump

Eric, any comments?

Matthew, seems you agree on this patch, may I have your ACK?

Thanks.

于 2011年03月11日 02:50, Matthew Garrett 写道:
> On Thu, Mar 10, 2011 at 09:50:28AM -0800, Eric W. Biederman wrote:
>
>> Move all EFI calls that the kernel does (on x86) into a special section
>> of the bzImage that the bootloader can run.  This works very well for
>> the x86 BIOS and it should also work very well for EFI.  Among other
>> things by having a special 32bit and a special 64bit section this solves
>> the what flavor of EFI problem are we running on problem.
>
> There's no benefit in calling any EFI methods in the kernel if we have
> no intention of making further calls later. If we intent on making
> further calls later then this approach doesn't work well.
>
>> Never perform any EFI calls once the kernel is initialized, last I
>> looked all of the EFI calls that were interesting to perform at runtime
>> were a subset of what ACPI can do, and ACPI is a easier to deal with
>> long term.
>
> With the exception of reboot, I don't see any overlap between the EFI
> runtime services and ACPI.
>
>> Kexec and kdump can easily pass the gather data from the first kernel to
>> the second kernel like we do for the normal bios paramsters today.
>
> Doing that's not a problem. The real problem is that passing a virtual
> map to EFI is a one-shot event. The information we need to provide to
> the second kernel isn't a set of parameters - it's the whole memory map,
> and we need to depend on the kernel to be able to set up the same map
> again.
>
>> As a fly in the ointment that leaves the question of how do we set EFI
>> variables.  It is needed functionality when we are installing, and
>> occasionally nice to have.  But it is a very rare slow path.  I would
>> isolate the EFI after the kernel has booted to exactly to that one case.
>> Either with a special driver or a some flavor of virtualization from
>> userspace like we used to do for video card initialization.
>
> Also capsule updating (not that we implement that at present, but
> vendors will want it). But, again, if you want to push this out to some
> sort of magic then we can just drop pretty much all of the kernel EFI
> support.
>
>> The current design of EFI in the x86 kernel is crap.  We seem to have
>> advanced past the early adopter hack anything together to make it work
>> stage.  So let's stop adding hacks and write something that won't give
>> us a long term support problems.
>
> We're using EFI exactly as it's designed to be used at the moment. The
> only problem is that nobody ever thought people would try to do anything
> like booting one OS into another OS that has different ideas about
> address space layout, but that's a problem with the spec and not our
> implementation.
>

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