[Xen-devel] [PATCH] libx86/CPUID: fix (not just) leaf 7 processing

[Xen-devel] [PATCH] libx86/CPUID: fix (not just) leaf 7 processing

[Jan Beulich]

For one, subleaves within the respective union shouldn't live in
separate sub-structures. And then x86_cpuid_policy_fill_native() should,
as it did originally, iterate over all subleaves here as well as over
all main leaves. Switch to using a "<= MIN()"-based approach similar to
that used in x86_cpuid_copy_to_buffer(). Also follow this for the
extended main leaves then.

Fixes: 1bd2b750537b ("libx86: Fix 32bit stubdom build of x86_cpuid_policy_fill_native()")
Fixes: 97e4ebdcd765 ("x86/CPUID: support leaf 7 subleaf 1 / AVX512_BF16")
Signed-off-by: Jan Beulich <jbeulich@suse.com>

--- a/xen/include/xen/lib/x86/cpuid.h
+++ b/xen/include/xen/lib/x86/cpuid.h
@@ -181,8 +181,7 @@ struct cpuid_policy
                 uint32_t _7d0;
                 struct { DECL_BITFIELD(7d0); };
             };
-        };
-        struct {
+
             /* Subleaf 1. */
             union {
                 uint32_t _7a1;
--- a/xen/lib/x86/cpuid.c
+++ b/xen/lib/x86/cpuid.c
@@ -71,8 +71,8 @@ void x86_cpuid_policy_fill_native(struct
     unsigned int i;
 
     cpuid_leaf(0, &p->basic.raw[0]);
-    for ( i = 1; i < min_t(unsigned int, ARRAY_SIZE(p->basic.raw),
-                           p->basic.max_leaf); ++i )
+    for ( i = 1; i <= MIN(p->basic.max_leaf,
+                          ARRAY_SIZE(p->basic.raw) - 1); ++i )
     {
         switch ( i )
         {
@@ -116,8 +116,8 @@ void x86_cpuid_policy_fill_native(struct
     {
         cpuid_count_leaf(7, 0, &p->feat.raw[0]);
 
-        for ( i = 1; i < min_t(unsigned int, ARRAY_SIZE(p->feat.raw),
-                               p->feat.max_subleaf); ++i )
+        for ( i = 1; i <= MIN(p->feat.max_subleaf,
+                              ARRAY_SIZE(p->feat.raw) - 1); ++i )
             cpuid_count_leaf(7, i, &p->feat.raw[i]);
     }
 
@@ -172,8 +172,8 @@ void x86_cpuid_policy_fill_native(struct
 
     /* Extended leaves. */
     cpuid_leaf(0x80000000, &p->extd.raw[0]);
-    for ( i = 1; i < min_t(unsigned int, ARRAY_SIZE(p->extd.raw),
-                           p->extd.max_leaf + 1 - 0x80000000); ++i )
+    for ( i = 1; i <= MIN(p->extd.max_leaf & 0xffffU,
+                          ARRAY_SIZE(p->extd.raw) - 1); ++i )
         cpuid_leaf(0x80000000 + i, &p->extd.raw[i]);
 
     x86_cpuid_policy_recalc_synth(p);

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Re: [Xen-devel] [PATCH] libx86/CPUID: fix (not just) leaf 7 processing

[Andrew Cooper]

On 23/03/2020 12:06, Jan Beulich wrote:
> For one, subleaves within the respective union shouldn't live in
> separate sub-structures.

Oops, and of course this stays hidden right now because there is no
overlap in known bits between subleaf 0 and 1 yet.

> And then x86_cpuid_policy_fill_native() should,
> as it did originally, iterate over all subleaves here as well as over
> all main leaves.

I was clearly asleep when writing that bugfix.  Again - it says hidden
because our local max_leaves are lower than ~all hardware these days.

>  Switch to using a "<= MIN()"-based approach similar to
> that used in x86_cpuid_copy_to_buffer(). Also follow this for the
> extended main leaves then.
>
> Fixes: 1bd2b750537b ("libx86: Fix 32bit stubdom build of x86_cpuid_policy_fill_native()")
> Fixes: 97e4ebdcd765 ("x86/CPUID: support leaf 7 subleaf 1 / AVX512_BF16")
> Signed-off-by: Jan Beulich <jbeulich@suse.com>

Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>