[PATCH v1.9 1/3] x86/amd: Use setup_force_cpu_cap() for BTC_NO

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

A XenServer feature in the process of being upstreamed is to be able to
re-caculate the guest CPU Policies at runtime, e.g. after a microcode load
and/or livepatch to expose new functionality.  Right now, upstream Xen only
rescans the Raw CPU Policy on microcode load.

One complication with recalculating the guest policies is that BTC_NO is
handled differently to other $FOO_NO bits, by using __set_bit() rather than
setup_force_cpu_cap().

For consistency, switch it to using setup_force_cpu_cap().  This doesn't
matter for upstream Xen right now, but it will ease upstream the feature.

Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
CC: Jan Beulich <JBeulich@xxxxxxxx>
CC: Roger Pau Monné <roger.pau@xxxxxxxxxx>

v2:
 * Rewrite the commit message.
---
 xen/arch/x86/cpu/amd.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/xen/arch/x86/cpu/amd.c b/xen/arch/x86/cpu/amd.c
index 805a8189e6cd..b3e12b084c56 100644
--- a/xen/arch/x86/cpu/amd.c
+++ b/xen/arch/x86/cpu/amd.c
@@ -1115,8 +1115,9 @@ static void cf_check init_amd(struct cpuinfo_x86 *c)
                 * Branch Type Confusion, but predate the allocation of the
                 * BTC_NO bit.  Fill it back in if we're not virtualised.
                 */
-               if (!cpu_has_hypervisor && !cpu_has(c, X86_FEATURE_BTC_NO))
-                       __set_bit(X86_FEATURE_BTC_NO, c->x86_capability);
+               if (c == &boot_cpu_data && !cpu_has_hypervisor &&
+                   !cpu_has(c, X86_FEATURE_BTC_NO))
+                       setup_force_cpu_cap(X86_FEATURE_BTC_NO);
                break;
        }
 
-- 
2.39.5