On Tue, Oct 31, 2017 at 3:31 PM, Dave Hansen <[email protected]> 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 <[email protected]> > Cc: Moritz Lipp <[email protected]> > Cc: Daniel Gruss <[email protected]> > Cc: Michael Schwarz <[email protected]> > Cc: Andy Lutomirski <[email protected]> > Cc: Linus Torvalds <[email protected]> > Cc: Kees Cook <[email protected]> > Cc: Hugh Dickins <[email protected]> > Cc: [email protected] > --- > > 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
