| From 6a012288d6906fee1dbc244050ade1dafe4a9c8d Mon Sep 17 00:00:00 2001 |
| From: Vlastimil Babka <vbabka@suse.cz> |
| Date: Thu, 23 Aug 2018 16:21:29 +0200 |
| Subject: x86/speculation/l1tf: Suggest what to do on systems with too much RAM |
| |
| From: Vlastimil Babka <vbabka@suse.cz> |
| |
| commit 6a012288d6906fee1dbc244050ade1dafe4a9c8d upstream. |
| |
| 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. |
| |
| Make the warning more helpful by suggesting the proper mem=X kernel boot |
| parameter to make it effective 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> |
| Signed-off-by: Vlastimil Babka <vbabka@suse.cz> |
| Acked-by: Michal Hocko <mhocko@suse.com> |
| Cc: "H . Peter Anvin" <hpa@zytor.com> |
| Cc: Linus Torvalds <torvalds@linux-foundation.org> |
| Cc: Andi Kleen <ak@linux.intel.com> |
| Cc: Dave Hansen <dave.hansen@intel.com> |
| Cc: stable@vger.kernel.org |
| Link: https://lkml.kernel.org/r/966571f0-9d7f-43dc-92c6-a10eec7a1254@suse.cz |
| Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| |
| --- |
| arch/x86/kernel/cpu/bugs.c | 4 ++++ |
| 1 file changed, 4 insertions(+) |
| |
| --- a/arch/x86/kernel/cpu/bugs.c |
| +++ b/arch/x86/kernel/cpu/bugs.c |
| @@ -686,6 +686,10 @@ static void __init l1tf_select_mitigatio |
| half_pa = (u64)l1tf_pfn_limit() << PAGE_SHIFT; |
| if (e820__mapped_any(half_pa, ULLONG_MAX - half_pa, E820_TYPE_RAM)) { |
| pr_warn("System has more than MAX_PA/2 memory. L1TF mitigation not effective.\n"); |
| + pr_info("You may make it effective by booting the kernel with mem=%llu parameter.\n", |
| + half_pa); |
| + pr_info("However, doing so will make a part of your RAM unusable.\n"); |
| + pr_info("Reading https://www.kernel.org/doc/html/latest/admin-guide/l1tf.html might help you decide.\n"); |
| return; |
| } |
| |