x86/xen: Fix __xen_hypercall_setfunc()

Hypercall detection is failing with xen_hypercall_intel() chosen even on
an AMD processor.  Looking at the disassembly, the call to
xen_get_vendor() was removed.

The check for boot_cpu_has(X86_FEATURE_CPUID) was used as a proxy for
the x86_vendor having been set.

When CONFIG_X86_REQUIRED_FEATURE_CPUID=y (the default value), DCE eliminates
the call to xen_get_vendor().  An uninitialized value 0 means
X86_VENDOR_INTEL, so the Intel function is always returned.

Remove the if and always call xen_get_vendor() to avoid this issue.

Fixes: 3d37d9396eb3 ("x86/cpufeatures: Add {REQUIRED,DISABLED} feature configs")
Suggested-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Jason Andryuk <jason.andryuk@amd.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Juergen Gross <jgross@suse.com>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: "Xin Li (Intel)" <xin@zytor.com>
Link: https://lore.kernel.org/r/20250410193106.16353-1-jason.andryuk@amd.com

diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
index 1b7710bd0d05113e6dc61c8201186e5d542705a0..53282dc7d5ac5be611d0a56f3693c36ca5d2f435 100644 (file)
--- a/arch/x86/xen/enlighten.c
+++ b/arch/x86/xen/enlighten.c
@@ -103,10 +103,6 @@ noinstr void *__xen_hypercall_setfunc(void)
        void (*func)(void);
 
        /*
-        * Xen is supported only on CPUs with CPUID, so testing for
-        * X86_FEATURE_CPUID is a test for early_cpu_init() having been
-        * run.
-        *
         * Note that __xen_hypercall_setfunc() is noinstr only due to a nasty
         * dependency chain: it is being called via the xen_hypercall static
         * call when running as a PVH or HVM guest. Hypercalls need to be
@@ -118,8 +114,7 @@ noinstr void *__xen_hypercall_setfunc(void)
         */
        instrumentation_begin();
 
-       if (!boot_cpu_has(X86_FEATURE_CPUID))
-               xen_get_vendor();
+       xen_get_vendor();
 
        if ((boot_cpu_data.x86_vendor == X86_VENDOR_AMD ||
             boot_cpu_data.x86_vendor == X86_VENDOR_HYGON))