lkml.org 
[lkml]   [2018]   [Aug]   [23]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH] x86/speculation/l1tf: suggest what to do on systems with too much RAM
Date
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 <vbabka@suse.cz>
---
arch/x86/kernel/cpu/bugs.c | 5 +++++
1 file changed, 5 insertions(+)

diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index cb4a16292aa7..4b820bb6c504 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -702,6 +702,11 @@ static void __init l1tf_select_mitigation(void)
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 up to %llu bytes of RAM unusable.\n",
+ ((u64) max_pfn << PAGE_SHIFT) - half_pa);
+ pr_info("Reading Documentation/admin-guide/l1tf.rst might help you decide.");
return;
}

--
2.18.0
\
 
 \ /
  Last update: 2018-08-23 16:28    [W:0.111 / U:0.728 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site