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) <pet...@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.
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