On Tue, Oct 31, 2017 at 3:31 PM, Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx> wrote: > > 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: 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 | 6 ++++-- > 1 file changed, 4 insertions(+), 2 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 2017-10-31 15:03:50.479119470 -0700 > +++ b/arch/x86/include/asm/tlbflush.h 2017-10-31 15:03:50.482119612 -0700 > @@ -258,9 +258,11 @@ 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 > + * all entries. Make sure that we _change_ the bit, regardless of nit: "... flush the all entries." Drop "the" in the line above? > * 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 CR3 value back: */ pre-existing nit: s/CR3/CR4/ -Kees -- Kees Cook Pixel Security -- 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>
