Re: [RFC PATCH v4 26/28] x86: Allow kexec to be used with SME

[Tom Lendacky]

On 3/1/2017 3:25 AM, Dave Young wrote:
> Hi Tom,

Hi Dave,

> On 02/17/17 at 10:43am, Tom Lendacky wrote:
> > On 2/17/2017 9:57 AM, Konrad Rzeszutek Wilk wrote:
> > > On Thu, Feb 16, 2017 at 09:47:55AM -0600, Tom Lendacky wrote:
> > > > Provide support so that kexec can be used to boot a kernel when SME is
> > > > enabled.
> > >
> > > Is the point of kexec and kdump to ehh, dump memory ? But if the
> > > rest of the memory is encrypted you won't get much, will you?
> >
> > Kexec can be used to reboot a system without going back through BIOS.
> > So you can use kexec without using kdump.
> >
> > For kdump, just taking a quick look, the option to enable memory
> > encryption can be provided on the crash kernel command line and then
>
> Is there a simple way to get the SME status? Probably add some sysfs
> file for this purpose.

Currently there is not.  I can look at adding something, maybe just the
sme_me_mask value, which if non-zero, would indicate SME is active.

> > crash kernel can would be able to copy the memory decrypted if the
> > pagetable is set up properly. It looks like currently ioremap_cache()
> > is used to map the old memory page.  That might be able to be changed
> > to a memremap() so that the encryption bit is set in the mapping. That
> > will mean that memory that is not marked encrypted (EFI tables, swiotlb
> > memory, etc) would not be read correctly.
>
> Manage to store info about those ranges which are not encrypted so that
> memremap can handle them?

I can look into whether something can be done in this area. Any input
you can provide as to what would be the best way/place to store the
range info so kdump can make use of it, would be greatly appreciated.

> > > Would it make sense to include some printk to the user if they
> > > are setting up kdump that they won't get anything out of it?
> >
> > Probably a good idea to add something like that.
>
> It will break kdump functionality, it should be fixed instead of
> just adding printk to warn user..

I do want kdump to work. I'll investigate further what can be done in
this area.

Thanks,
Tom

> Thanks
> Dave