Commit-ID: 6a012288d6906fee1dbc244050ade1dafe4a9c8d
Gitweb: https://git.kernel.org/tip/6a012288d6906fee1dbc244050ade1dafe4a9c8d
Author: Vlastimil Babka <vbabka@xxxxxxx>
AuthorDate: Thu, 23 Aug 2018 16:21:29 +0200
Committer: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
CommitDate: Fri, 24 Aug 2018 15:55:17 +0200
x86/speculation/l1tf: Suggest what to do on systems with too much RAM
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@xxxxxxxx>
Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
Cc: "H . Peter Anvin" <hpa@xxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Andi Kleen <ak@xxxxxxxxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Link: https://lkml.kernel.org/r/966571f0-9d7f-43dc-92c6-a10eec7a1254@xxxxxxx
---
arch/x86/kernel/cpu/bugs.c | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index cb4a16292aa7..4c2313d0b9ca 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -702,6 +702,10 @@ 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 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;
}
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