Messages in this thread | | | From | Kees Cook <> | Date | Tue, 31 Oct 2017 16:31:43 -0700 | Subject | Re: [PATCH 05/23] x86, mm: document X86_CR4_PGE toggling behavior |
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On Tue, Oct 31, 2017 at 3:31 PM, Dave Hansen <dave.hansen@linux.intel.com> 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@linux.intel.com> > Cc: Moritz Lipp <moritz.lipp@iaik.tugraz.at> > Cc: Daniel Gruss <daniel.gruss@iaik.tugraz.at> > Cc: Michael Schwarz <michael.schwarz@iaik.tugraz.at> > Cc: Andy Lutomirski <luto@kernel.org> > Cc: Linus Torvalds <torvalds@linux-foundation.org> > Cc: Kees Cook <keescook@google.com> > Cc: Hugh Dickins <hughd@google.com> > Cc: x86@kernel.org > --- > > 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
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