x86/gen-cpuid: Distinguish default vs max in feature annotations
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Message ID 20200508152729.14295-1-andrew.cooper3@citrix.com
State New
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  • x86/gen-cpuid: Distinguish default vs max in feature annotations
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Commit Message

Andrew Cooper May 8, 2020, 3:27 p.m. UTC
Allow lowercase a/s/h to be used to annotate a non-default feature.

However, until the toolstack migration logic is fixed, it is not safe to
activate yet.  Tolerate the annotations, but ignore them for now.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Jan Beulich <jbeulich@suse.com>
---
CC: Jan Beulich <JBeulich@suse.com>
CC: Wei Liu <wl@xen.org>
CC: Roger Pau Monné <roger.pau@citrix.com>

This patch has been pending the toolstack work for several months now, and we
want to start using the max tags for x86 emul work.
---
 xen/include/public/arch-x86/cpufeatureset.h | 2 ++
 xen/tools/gen-cpuid.py                      | 5 +++++
 2 files changed, 7 insertions(+)

Comments

Jan Beulich May 11, 2020, 7:43 a.m. UTC | #1
On 08.05.2020 17:27, Andrew Cooper wrote:
> @@ -133,9 +134,13 @@ def crunch_numbers(state):
>      state.hvm_shadow_def = state.pv_def | state.raw['S']
>      state.hvm_hap_def = state.hvm_shadow_def | state.raw['H']
>  
> +    # TODO: Ignore def/max split until the toolstack migration logic is fixed
>      state.pv_max = state.pv_def
>      state.hvm_shadow_max = state.hvm_shadow_def
>      state.hvm_hap_max = state.hvm_hap_def
> +    # state.pv_max = state.raw['A'] | state.raw['a']
> +    # state.hvm_shadow_max = state.pv_max | state.raw['S'] | state.raw['s']
> +    # state.hvm_hap_max = state.hvm_shadow_max | state.raw['H'] | state.raw['h']

While in comment form it doesn't matter yet, for actually enabling
this it would seem to me to be more expressive as

    state.pv_max = state.pv_def | state.raw['a']
    state.hvm_shadow_max = state.hvm_shadow_def | state.pv_max | state.raw['s']
    state.hvm_hap_max = state.hvm_hap_def | state.hvm_shadow_max | state.raw['h']

Thoughts?

Jan
Andrew Cooper May 15, 2020, 1:19 p.m. UTC | #2
On 11/05/2020 08:43, Jan Beulich wrote:
> [CAUTION - EXTERNAL EMAIL] DO NOT reply, click links, or open attachments unless you have verified the sender and know the content is safe.
>
> On 08.05.2020 17:27, Andrew Cooper wrote:
>> @@ -133,9 +134,13 @@ def crunch_numbers(state):
>>      state.hvm_shadow_def = state.pv_def | state.raw['S']
>>      state.hvm_hap_def = state.hvm_shadow_def | state.raw['H']
>>  
>> +    # TODO: Ignore def/max split until the toolstack migration logic is fixed
>>      state.pv_max = state.pv_def
>>      state.hvm_shadow_max = state.hvm_shadow_def
>>      state.hvm_hap_max = state.hvm_hap_def
>> +    # state.pv_max = state.raw['A'] | state.raw['a']
>> +    # state.hvm_shadow_max = state.pv_max | state.raw['S'] | state.raw['s']
>> +    # state.hvm_hap_max = state.hvm_shadow_max | state.raw['H'] | state.raw['h']
> While in comment form it doesn't matter yet, for actually enabling
> this it would seem to me to be more expressive as
>
>     state.pv_max = state.pv_def | state.raw['a']
>     state.hvm_shadow_max = state.hvm_shadow_def | state.pv_max | state.raw['s']
>     state.hvm_hap_max = state.hvm_hap_def | state.hvm_shadow_max | state.raw['h']
>
> Thoughts?

The format/layout of metadata prohibits that from having any kind of
difference.

Furthermore, expressing it this way doesn't require anyone to look at
the *_def derivation to figure out what is going on.

I'm going to commit it in this form, but will tidy it up to be properly
tabulated in a future patch, to make it easier to read.

~Andrew

Patch
diff mbox series

diff --git a/xen/include/public/arch-x86/cpufeatureset.h b/xen/include/public/arch-x86/cpufeatureset.h
index e2749245f3..0ffab6c57b 100644
--- a/xen/include/public/arch-x86/cpufeatureset.h
+++ b/xen/include/public/arch-x86/cpufeatureset.h
@@ -87,6 +87,8 @@  enum {
  *   'A' = All guests.
  *   'S' = All HVM guests (not PV guests).
  *   'H' = HVM HAP guests (not PV or HVM Shadow guests).
+ *   Upper case => Available by default
+ *   Lower case => Can be opted-in to, but not available by default.
  */
 
 /* Intel-defined CPU features, CPUID level 0x00000001.edx, word 0 */
diff --git a/xen/tools/gen-cpuid.py b/xen/tools/gen-cpuid.py
index af5610a5e6..d90a2d85c7 100755
--- a/xen/tools/gen-cpuid.py
+++ b/xen/tools/gen-cpuid.py
@@ -23,6 +23,7 @@  def __init__(self, input, output):
         self.raw = {
             '!': set(),
             'A': set(), 'S': set(), 'H': set(),
+            'a': set(), 's': set(), 'h': set(),
         }
 
         # State calculated
@@ -133,9 +134,13 @@  def crunch_numbers(state):
     state.hvm_shadow_def = state.pv_def | state.raw['S']
     state.hvm_hap_def = state.hvm_shadow_def | state.raw['H']
 
+    # TODO: Ignore def/max split until the toolstack migration logic is fixed
     state.pv_max = state.pv_def
     state.hvm_shadow_max = state.hvm_shadow_def
     state.hvm_hap_max = state.hvm_hap_def
+    # state.pv_max = state.raw['A'] | state.raw['a']
+    # state.hvm_shadow_max = state.pv_max | state.raw['S'] | state.raw['s']
+    # state.hvm_hap_max = state.hvm_shadow_max | state.raw['H'] | state.raw['h']
 
     #
     # Feature dependency information.