Commit 6a012288 authored by Vlastimil Babka's avatar Vlastimil Babka Committed by Thomas Gleixner

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] default avatarMichal Hocko <>
Signed-off-by: default avatarVlastimil Babka <>
Acked-by: default avatarMichal Hocko <>
Cc: "H . Peter Anvin" <>
Cc: Linus Torvalds <>
Cc: Andi Kleen <>
Cc: Dave Hansen <>
parent b0a182f8
......@@ -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",
pr_info("However, doing so will make a part of your RAM unusable.\n");
pr_info("Reading might help you decide.\n");
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