On 08/24/2018 09:32 AM, Vlastimil Babka wrote:

On 08/23/2018 09:27 PM, Michal Hocko wrote:

quoted

On Thu 23-08-18 16:28:12, Vlastimil Babka wrote:

quoted

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] https://bugzilla.suse.com/show_bug.cgi?id=1105536

Suggested-by: Michal Hocko <mhocko@suse.com>
Cc: stable@vger.kernel.org
Signed-off-by: Vlastimil Babka <redacted>

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.

quoted

Acked-by: Michal Hocko <mhocko@suse.com>

Thanks! Here's a v2:

Just realized that kvm printk's refer to the online version at
https://www.kernel.org/doc/html/latest/admin-guide/l1tf.html
which should be easier for the users of distro kernels, should I change
that?