linux-kernel - Re: [PATCH 6/6] x86: fixes some bugs about EFI memory map handling

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Date:	Fri, 25 Jan 2008 21:58:34 +0800
From:	"huang ying" <huang.ying.caritas@...il.com>
To:	"Ingo Molnar" <mingo@...e.hu>
Cc:	"Huang, Ying" <ying.huang@...el.com>,
	"Ingo Molnar" <mingo@...hat.com>, "H. Peter Anvin" <hpa@...or.com>,
	"Thomas Gleixner" <tglx@...utronix.de>, "Andi Kleen" <ak@...e.de>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 6/6] x86: fixes some bugs about EFI memory map handling

On Jan 25, 2008 5:50 PM, Ingo Molnar <mingo@...e.hu> wrote:
>
> * Huang, Ying <ying.huang@...el.com> wrote:
>
> > On Fri, 2008-01-25 at 10:31 +0100, Ingo Molnar wrote:
> > > * Huang, Ying <ying.huang@...el.com> wrote:
> > >
> > > > This patch fixes some bugs of EFI memory handing code.
> > > >
> > > > - On x86_64, it is possible that EFI memory map can not be mapped via
> > > >   identity map, so efi_map_memmap is removed, just use early_ioremap.
> > > >
> > > > - On i386, the EFI memory map mapping take effect cross paging_init,
> > > >   so it is not necessary to use efi_map_memmap.
> > > >
> > > > - EFI memory map is unmapped in efi_enter_virtual_mode to avoid
> > > >   early_ioremap leak.
> > >
> > > thanks, applied.
> > >
> > > btw., it would be nice to consolidate this some more. Why is there a
> > > separate efi_ioremap(), which is mapped to ioremap() on 32-bit, and
> > > which is mapped to a fixmap based special mapper on 64-bit?
> > >
> > > To me it appears this wants to be ioremap() on both 64-bit and
> > > 32-bit, and we could remove efi_ioremap() altogether. Hm?
> >
> > To support kexec, I want to map the EFI memory area on same virtual
> > address on different boot of different version of kernel. Then, the
> > EFI runtime service will always get the same execution environment.
> > This is because a weakness of EFI runtime service, it can not reset
> > its execution environment, except reboot.
>
> so this basically means that on 32-bit kexec wont work right - i.e. only
> 64-bit has been enhanced this way? What am i missing?

Strictly, I should say on 32-bit, EFI runtime service won't work in
kexeced kernel. That is, on EFI 32 platform, it is possible that:

- Boot kernel A with EFI runtime service
- kexec kernel B without EFI runtime service (such as with noefi in
kernel command line)

I suspect this method can be used on 32-bit platform. Because the
fixmap area on 32-bit is more limited than 64-bit. And because
identity map area on 32-bit is too limited, it is possible that all
EFI runtime code, data, IO areas need to be mapped via  fixmap.

Best Regards,
Huang Ying
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