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

[Dave Young]

Hi Tom,

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.

> 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?

> 
> > 
> > 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..

Thanks
Dave