lkml.org 
[lkml]   [2017]   [Nov]   [29]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    Patch in this message
    /
    Date
    From
    SubjectRe: [PATCH 4/6] x86/mm/kaiser: Support PCID without INVPCID
    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_\@:
    /*
    \
     
     \ /
      Last update: 2017-11-29 12:49    [W:4.139 / U:0.136 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site