Re: [PATCH] x86/speculation/l1tf: suggest what to do on systems with too much RAM

From: Vlastimil Babka
Date: Fri Aug 24 2018 - 08:11:02 EST

On 08/24/2018 12:36 PM, Vlastimil Babka wrote:
> On 08/24/2018 09:32 AM, Vlastimil Babka wrote:
>> On 08/23/2018 09:27 PM, Michal Hocko wrote:
>>> On Thu 23-08-18 16:28:12, Vlastimil Babka wrote:
>>>> Two users have reported [1] that they have an "extremely unlikely" system
>>>> with more than MAX_PA/2 memory and L1TF mitigation is not effective. Let's
>>>> make the warning more helpful by suggesting the proper mem=X kernel boot param,
>>>> a rough calculation of how much RAM can be lost (not precise if there's holes
>>>> between MAX_PA/2 and max_pfn in the e820 map) and a link to the L1TF document
>>>> to help decide if the mitigation is worth the unusable RAM.
>>>> [1]
>>>> Suggested-by: Michal Hocko <mhocko@xxxxxxxx>
>>>> Cc: stable@xxxxxxxxxxxxxxx
>>>> Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx>
>>> I wouldn't bother with max_pfn-half_pa part but other than that this is
>>> much more useful than the original message.
>> Right, and it causes build failures on some configs.
>>> Acked-by: Michal Hocko <mhocko@xxxxxxxx>
>> Thanks! Here's a v2:
> Just realized that kvm printk's refer to the online version at
> which should be easier for the users of distro kernels, should I change
> that?

FWIW, if it's not possible to amend anymore...