On Wed, Nov 29, 2017 at 11:33:05AM +0100, Peter Zijlstra wrote:
> XXX we could do a much larger ALTERNATIVE, there is no point in
> testing the mask if we don't have PCID support.
This.
> @@ -220,7 +215,27 @@ For 32-bit we have the following convent
> .macro SWITCH_TO_USER_CR3 scratch_reg:req
> STATIC_JUMP_IF_FALSE .Lend_\@, kaiser_enabled_key, def=1
> mov %cr3, \scratch_reg
> - ADJUST_USER_CR3 \scratch_reg
> +
> + /*
> + * Test if the ASID needs a flush.
> + */
> + push \scratch_reg /* preserve CR3 */
> + andq $(0x7FF), \scratch_reg /* mask ASID */
> + bt \scratch_reg, PER_CPU_VAR(user_asid_flush_mask)
> + jnc .Lnoflush_\@
> +
> + /* Flush needed, clear the bit */
> + btr \scratch_reg, PER_CPU_VAR(user_asid_flush_mask)
> + pop \scratch_reg /* original CR3 */
> + jmp .Ldo_\@
> +
> +.Lnoflush_\@:
> + pop \scratch_reg /* original CR3 */
> + ALTERNATIVE "", "bts $63, \scratch_reg", X86_FEATURE_PCID
> +
> +.Ldo_\@:
> + /* Flip the PGD and ASID to the user version */
> + orq $(KAISER_SWITCH_MASK), \scratch_reg
> mov \scratch_reg, %cr3
> .Lend_\@:
> .endm
Something like so seems to actually compile and generate sensible code,
not tested it though.
--- a/arch/x86/entry/calling.h
+++ b/arch/x86/entry/calling.h
@@ -216,6 +216,8 @@ For 32-bit we have the following convent
STATIC_JUMP_IF_FALSE .Lend_\@, kaiser_enabled_key, def=1
mov %cr3, \scratch_reg
+ ALTERNATIVE "jmp .Ldo_\@", "", X86_FEATURE_PCID
+
/*
* Test if the ASID needs a flush.
*/
@@ -231,7 +233,7 @@ For 32-bit we have the following convent
.Lnoflush_\@:
pop \scratch_reg /* original CR3 */
- ALTERNATIVE "", "bts $63, \scratch_reg", X86_FEATURE_PCID
+ bts $63, \scratch_reg
.Ldo_\@:
/* Flip the PGD and ASID to the user version */
@@ -266,6 +268,8 @@ For 32-bit we have the following convent
.macro RESTORE_CR3 scratch_reg:req save_reg:req
STATIC_JUMP_IF_FALSE .Lend_\@, kaiser_enabled_key, def=1
+ ALTERNATIVE "jmp .Ldo_\@", "", X86_FEATURE_PCID
+
/* ASID bit 11 is for user */
bt $11, \save_reg
/*
@@ -287,7 +291,7 @@ For 32-bit we have the following convent
jmp .Ldo_\@
.Lnoflush_\@:
- ALTERNATIVE "", "bts $63, \save_reg", X86_FEATURE_PCID
+ bts $63, \save_reg
.Ldo_\@:
/*
