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

Tom Lendacky
2017-03-06T18:19:59Z

+kexec-list

On 3/6/2017 11:58 AM, Tom Lendacky wrote:
> 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
>>