From: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx> The comment says it all here. The problem here is that the X86_CR4_PGE bit affects all PCIDs in a way that is totally obscure. This makes it easier for someone to find if grepping for PCID- related stuff and documents the hardware behavior that we are depending on. Signed-off-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx> Cc: Moritz Lipp <moritz.lipp@xxxxxxxxxxxxxx> Cc: Daniel Gruss <daniel.gruss@xxxxxxxxxxxxxx> Cc: Michael Schwarz <michael.schwarz@xxxxxxxxxxxxxx> Cc: Richard Fellner <richard.fellner@xxxxxxxxxxxxxxxxx> Cc: Andy Lutomirski <luto@xxxxxxxxxx> Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Cc: Kees Cook <keescook@xxxxxxxxxx> Cc: Hugh Dickins <hughd@xxxxxxxxxx> Cc: x86@xxxxxxxxxx --- b/arch/x86/include/asm/tlbflush.h | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) diff -puN arch/x86/include/asm/tlbflush.h~kaiser-prep-document-cr4-pge-behavior arch/x86/include/asm/tlbflush.h --- a/arch/x86/include/asm/tlbflush.h~kaiser-prep-document-cr4-pge-behavior 2017-11-08 10:45:26.994681401 -0800 +++ b/arch/x86/include/asm/tlbflush.h 2017-11-08 10:45:26.997681401 -0800 @@ -257,10 +257,12 @@ static inline void __native_flush_tlb_gl */ WARN_ON_ONCE(!(cr4 & X86_CR4_PGE)); /* - * Architecturally, any _change_ to X86_CR4_PGE will fully flush the - * TLB of all entries including all entries in all PCIDs and all - * global pages. Make sure that we _change_ the bit, regardless of + * Architecturally, any _change_ to X86_CR4_PGE will fully flush + * all entries. Make sure that we _change_ the bit, regardless of * whether we had X86_CR4_PGE set in the first place. + * + * Note that just toggling PGE *also* flushes all entries from all + * PCIDs, regardless of the state of X86_CR4_PCIDE. */ native_write_cr4(cr4 ^ X86_CR4_PGE); /* Put original CR4 value back: */ _ -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
