host_cpu_policy already fetched the SVM CPUIDs, use it instead of open-coding cpuid.

Signed-off-by: Teddy Astie <teddy.astie@vates.tech>
---
It very likely doesn't work right now, as host_cpu_policy is not evaluated at this point
(start_svm is unfortunately called before calculate_host_policy). So this is mostly a intent
rather than something ready.

There are also some other things I would like to improve on this, but not sure on the approach.

It would be nice to move svm_feature_flags to host_cpu_policy, alike other
bitmap-like leafs we have in cpu_policy. IOW move most of arch/x86/include/asm/hvm/svm/svm.h
to cpu_policy infrastructure, which could also serve later for properly managing nested SVM
features of a guest.

And also move most policy calculation to it (feature dependencies check, erratas, ...).
For instance check for AMD_ERRATUM_170 in cpu policy code, and mask cpu_has_svm_flushbyasid
if CPU is affected, trying to declutter SVM logic from some errata checks.

 xen/arch/x86/hvm/svm/asid.c          | 3 ++-
 xen/arch/x86/hvm/svm/svm.c           | 4 ++--
 xen/include/xen/lib/x86/cpu-policy.h | 5 ++++-
 3 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/xen/arch/x86/hvm/svm/asid.c b/xen/arch/x86/hvm/svm/asid.c
index 03f98b7a8b..0af5874b76 100644
--- a/xen/arch/x86/hvm/svm/asid.c
+++ b/xen/arch/x86/hvm/svm/asid.c
@@ -5,6 +5,7 @@
  */
 
 #include <asm/amd.h>
+#include <asm/cpu-policy.h>
 #include <asm/hvm/nestedhvm.h>
 #include <asm/hvm/svm/svm.h>
 
@@ -16,7 +17,7 @@ void svm_asid_init(const struct cpuinfo_x86 *c)
 
     /* Check for erratum #170, and leave ASIDs disabled if it's present. */
     if ( !cpu_has_amd_erratum(c, AMD_ERRATUM_170) )
-        nasids = cpuid_ebx(0x8000000aU);
+        nasids = host_cpu_policy.extd.nasid;
 
     hvm_asid_init(nasids);
 }
diff --git a/xen/arch/x86/hvm/svm/svm.c b/xen/arch/x86/hvm/svm/svm.c
index 2d7c598ffe..e3f503c328 100644
--- a/xen/arch/x86/hvm/svm/svm.c
+++ b/xen/arch/x86/hvm/svm/svm.c
@@ -15,6 +15,7 @@
 
 #include <asm/amd.h>
 #include <asm/apic.h>
+#include <asm/cpu-policy.h>
 #include <asm/cpufeature.h>
 #include <asm/current.h>
 #include <asm/debugreg.h>
@@ -2494,8 +2495,7 @@ const struct hvm_function_table * __init start_svm(void)
 
     setup_vmcb_dump();
 
-    if ( boot_cpu_data.extended_cpuid_level >= 0x8000000aU )
-        svm_feature_flags = cpuid_edx(0x8000000aU);
+    svm_feature_flags = host_cpu_policy.extd.svm_feature_flags;
 
     printk("SVM: Supported advanced features:\n");
 
diff --git a/xen/include/xen/lib/x86/cpu-policy.h b/xen/include/xen/lib/x86/cpu-policy.h
index f94f23e159..1e639ae713 100644
--- a/xen/include/xen/lib/x86/cpu-policy.h
+++ b/xen/include/xen/lib/x86/cpu-policy.h
@@ -270,7 +270,10 @@ struct cpu_policy
             uint32_t /* d */:32;
 
             uint64_t :64, :64; /* Leaf 0x80000009. */
-            uint64_t :64, :64; /* Leaf 0x8000000a - SVM rev and features. */
+
+            /* Leaf 0x8000000a - SVM rev and features. */
+            uint32_t :32, nasid:32, :32, svm_feature_flags:32;
+
             uint64_t :64, :64; /* Leaf 0x8000000b. */
             uint64_t :64, :64; /* Leaf 0x8000000c. */
             uint64_t :64, :64; /* Leaf 0x8000000d. */
-- 
2.51.2



--
Teddy Astie | Vates XCP-ng Developer

XCP-ng & Xen Orchestra - Vates solutions

web: https://vates.tech

On 08.12.2025 15:58, Teddy Astie wrote:
> host_cpu_policy already fetched the SVM CPUIDs, use it instead of open-coding cpuid.
> 
> Signed-off-by: Teddy Astie <teddy.astie@vates.tech>
> ---
> It very likely doesn't work right now, as host_cpu_policy is not evaluated at this point
> (start_svm is unfortunately called before calculate_host_policy). So this is mostly a intent
> rather than something ready.
> 
> There are also some other things I would like to improve on this, but not sure on the approach.
> 
> It would be nice to move svm_feature_flags to host_cpu_policy, alike other
> bitmap-like leafs we have in cpu_policy. IOW move most of arch/x86/include/asm/hvm/svm/svm.h
> to cpu_policy infrastructure, which could also serve later for properly managing nested SVM
> features of a guest.

See https://lists.xen.org/archives/html/xen-devel/2024-06/msg01546.html

Jan