Messages in this thread | | | Date | Wed, 29 Nov 2017 21:02:12 +0100 | From | Borislav Petkov <> | Subject | Re: [PATCH 5/6] x86/mm/kaiser: Optimize RESTORE_CR3 |
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On Wed, Nov 29, 2017 at 11:33:06AM +0100, Peter Zijlstra wrote: > Currently RESTORE_CR3 does an unconditional flush > (SAVE_AND_SWITCH_TO_KERNEL_CR3 does not set bit 63 on \save_reg). > > When restoring to a user ASID, check the user_asid_flush_mask to see > if we can avoid the flush. > > For kernel ASIDs we can unconditionaly avoid the flush, since we do > explicit flushes for them. > > Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> > --- > arch/x86/entry/calling.h | 29 +++++++++++++++++++++++++++-- > arch/x86/entry/entry_64.S | 4 ++-- > 2 files changed, 29 insertions(+), 4 deletions(-) > > --- a/arch/x86/entry/calling.h > +++ b/arch/x86/entry/calling.h > @@ -263,8 +263,33 @@ For 32-bit we have the following convent > .Ldone_\@: > .endm > > -.macro RESTORE_CR3 save_reg:req > +.macro RESTORE_CR3 scratch_reg:req save_reg:req > STATIC_JUMP_IF_FALSE .Lend_\@, kaiser_enabled_key, def=1 > + > + /* ASID bit 11 is for user */ > + bt $11, \save_reg
<---- newline here.
> + /* > + * KERNEL pages can always resume with NOFLUSH as we do > + * explicit flushes. > + */ > + jnc .Lnoflush_\@ > + > + /* > + * Check if there's a pending flush for the user ASID we're > + * about to set. > + */ > + movq \save_reg, \scratch_reg > + andq $(0x7FF), \scratch_reg > + bt \scratch_reg, PER_CPU_VAR(user_asid_flush_mask) > + jnc .Lnoflush_\@ > + > + btr \scratch_reg, PER_CPU_VAR(user_asid_flush_mask) > + jmp .Ldo_\@
Can you save yourself one of the BT-insns?
... andq $(0x7FF), \scratch_reg btr \scratch_reg, PER_CPU_VAR(user_asid_flush_mask) jnc .Lnoflush_\@ jmp .Ldo_\@ ...
or am I missing a case?
-- Regards/Gruss, Boris.
Good mailing practices for 400: avoid top-posting and trim the reply.
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