On Fri, Dec 01, 2023 at 11:59:54AM -0800, Josh Poimboeuf wrote: > On Fri, Oct 27, 2023 at 07:38:59AM -0700, Pawan Gupta wrote: > > The VERW mitigation at exit-to-user is enabled via a static branch > > mds_user_clear. This static branch is never toggled after boot, and can > > be safely replaced with an ALTERNATIVE() which is convenient to use in > > asm. > > > > Switch to ALTERNATIVE() to use the VERW mitigation late in exit-to-user > > path. Also remove the now redundant VERW in exc_nmi() and > > arch_exit_to_user_mode(). > > > > Signed-off-by: Pawan Gupta <pawan.kumar.gupta@xxxxxxxxxxxxxxx> > > --- > > Documentation/arch/x86/mds.rst | 38 +++++++++++++++++++++++++----------- > > arch/x86/include/asm/entry-common.h | 1 - > > arch/x86/include/asm/nospec-branch.h | 12 ------------ > > arch/x86/kernel/cpu/bugs.c | 15 ++++++-------- > > arch/x86/kernel/nmi.c | 2 -- > > arch/x86/kvm/vmx/vmx.c | 2 +- > > 6 files changed, 34 insertions(+), 36 deletions(-) > > > > diff --git a/Documentation/arch/x86/mds.rst b/Documentation/arch/x86/mds.rst > > index e73fdff62c0a..a5c5091b9ccd 100644 > > --- a/Documentation/arch/x86/mds.rst > > +++ b/Documentation/arch/x86/mds.rst > > @@ -95,6 +95,9 @@ The kernel provides a function to invoke the buffer clearing: > > > > mds_clear_cpu_buffers() > > > > +Also macro CLEAR_CPU_BUFFERS is meant to be used in ASM late in exit-to-user > > +path. This macro works for cases where GPRs can't be clobbered. > > What does this last sentence mean? Is it trying to say that the macro > doesn't clobber registers (other than ZF)? Yes. I will rephrase it to say that macro doesn't clobber registers other than ZF.
