linux-kernel - Re: [PATCH v4 06/12] efi: export efi runtime memory mapping to sysfs

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Message-ID: <20131127030706.GB11852@dhcp-16-126.nay.redhat.com>
Date:	Wed, 27 Nov 2013 11:07:06 +0800
From:	Dave Young <dyoung@...hat.com>
To:	Matt Fleming <matt@...sole-pimps.org>
Cc:	linux-kernel@...r.kernel.org, linux-efi@...r.kernel.org,
	x86@...nel.org, mjg59@...f.ucam.org, hpa@...or.com,
	James.Bottomley@...senPartnership.com, vgoyal@...hat.com,
	ebiederm@...ssion.com, horms@...ge.net.au,
	kexec@...ts.infradead.org, bp@...en8.de, greg@...ah.com,
	toshi.kani@...com
Subject: Re: [PATCH v4 06/12] efi: export efi runtime memory mapping to sysfs

On 11/26/13 at 07:30pm, Matt Fleming wrote:
> On Tue, 26 Nov, at 01:57:51PM, Dave Young wrote:
> > kexec kernel will need exactly same mapping for
> > efi runtime memory ranges. Thus here export the
> > runtime ranges mapping to sysfs, kexec-tools
> > will assemble them and pass to 2nd kernel via
> > setup_data.
> > 
> > Introducing a new directly /sys/firmware/efi/runtime-map
> 
> I'm not sure why the word "directly" is used here?

should be directory, will fix.

> 
> > Just like /sys/firmware/memmap. Containing below attribute
> > in each file of that directory:
> > attribute  num_pages  phys_addr  type  virt_addr
> > 
> > It will not work for efi 32bit. Only x86_64 currently.
>  
> Actually, exporting the tables does work for 32-bit, right? It's just
> that kexec doesn't work for 32-bit EFI?

It does not make sense to export them for 32-bit because we do not
support kexec efi on 32-bit. Will change the description to below:

"kexec efi boot on 32-bit is not supported so I only export the tables
for 64-bit efi system."

> 
> > Matt: s/efi-runtime-map.c/runtime-map.c
> >       change dir name to runtime-map
> > update to use desc_size in efi_runtime_map
> > cleaup the code, add function efi_save_runtime_map
> > improve err handling
> > 
> > Signed-off-by: Dave Young <dyoung@...hat.com>
> > ---
> >  .../ABI/testing/sysfs-firmware-efi-runtime-map     |  45 +++++
> >  arch/x86/platform/efi/efi.c                        |  26 +++
> >  drivers/firmware/efi/Kconfig                       |  10 ++
> >  drivers/firmware/efi/Makefile                      |   1 +
> >  drivers/firmware/efi/efi.c                         |   3 +-
> >  drivers/firmware/efi/runtime-map.c                 | 199 +++++++++++++++++++++
> >  include/linux/efi.h                                |   6 +
> >  7 files changed, 289 insertions(+), 1 deletion(-)
> >  create mode 100644 Documentation/ABI/testing/sysfs-firmware-efi-runtime-map
> >  create mode 100644 drivers/firmware/efi/runtime-map.c
> > 
> > diff --git a/Documentation/ABI/testing/sysfs-firmware-efi-runtime-map b/Documentation/ABI/testing/sysfs-firmware-efi-runtime-map
> > new file mode 100644
> > index 0000000..dab8d41
> > --- /dev/null
> > +++ b/Documentation/ABI/testing/sysfs-firmware-efi-runtime-map
> > @@ -0,0 +1,45 @@
> > +What:		/sys/firmware/efi/runtime-map/
> > +Date:		Oct 2013
> > +Contact:	Dave Young <dyoung@...hat.com>
> > +Description:
> > +		Switching efi runtime services to virtual mode requires
> > +		that all efi memory ranges which has the runtime attribute
> > +		bit set to be mapped to virtual addresses.
> > +
> > +		In kexec kernel kernel can not entering virtual mode again
> > +		because there's a limitation that SetVirtualAddressMap can
> > +		only be called once for entering virtual mode. But kexec
> > +		kernel still need maintain same physical address to virtual
> > +		address mapping as the 1st kernel. The mappings are exported
> > +		to sysfs so userspace tools can reassemble them and pass them
> > +		into kexec kernel.
> 
> How about,
> 
> 		"The efi runtime services can only be switched to virtual
> 		 mode once without rebooting. The kexec kernel must maintain
> 		 the same physical to virtual address mappings as the first
> 		 kernel. The mappings are exported to sysfs so userspace tools
> 		 can reassemble them and pass them into the kexec kernel."
> 
> ?

Excellent, will above.

> 
> > +		/sys/firmware/efi/runtim-map/ is what kernel export for
> 
> 				^^ runtime-map/

Will fix the typo.

Thanks for review
Dave
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