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_\@: /* -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
