4.9-stable review patch. If anyone has any objections, please let me know. ------------------ From: Vlastimil Babka <vbabka@xxxxxxx> 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@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 Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- 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 @@ -685,6 +685,10 @@ static void __init l1tf_select_mitigatio half_pa = (u64)l1tf_pfn_limit() << PAGE_SHIFT; if (e820_any_mapped(half_pa, ULLONG_MAX - half_pa, E820_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; }
