Commit-ID: 6a012288d6906fee1dbc244050ade1dafe4a9c8d Gitweb: https://git.kernel.org/tip/6a012288d6906fee1dbc244050ade1dafe4a9c8d Author: Vlastimil Babka <[email protected]> AuthorDate: Thu, 23 Aug 2018 16:21:29 +0200 Committer: Thomas Gleixner <[email protected]> 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 <[email protected]> Signed-off-by: Vlastimil Babka <[email protected]> Acked-by: Michal Hocko <[email protected]> Cc: "H . Peter Anvin" <[email protected]> Cc: Linus Torvalds <[email protected]> Cc: Andi Kleen <[email protected]> Cc: Dave Hansen <[email protected]> Cc: [email protected] Link: https://lkml.kernel.org/r/[email protected] --- 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; }
