[Xen-devel] [PATCH] tools/libxc: Properly increment ApicIdCoreSize field on AMD

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

Current code incorrectly adds 1 to full register instead of
incrementing the field in bits 15:12.

Signed-off-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
---
 tools/libxc/xc_cpuid_x86.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/tools/libxc/xc_cpuid_x86.c b/tools/libxc/xc_cpuid_x86.c
index 84f4e08..fbbac9e 100644
--- a/tools/libxc/xc_cpuid_x86.c
+++ b/tools/libxc/xc_cpuid_x86.c
@@ -331,7 +331,8 @@ static void amd_xc_cpuid_policy(xc_interface *xch,
          * ECX[15:12] is ApicIdCoreSize: ECX[7:0] is NumberOfCores (minus one).
          * Update to reflect vLAPIC_ID = vCPU_ID * 2.
          */
-        regs[2] = ((regs[2] & 0xf000u) + 1) | ((regs[2] & 0xffu) << 1) | 1u;
+        regs[2] = ((regs[2] + (1u << 12)) & 0xf000u) |
+                  ((regs[2] & 0xffu) << 1) | 1u;
         break;
 
     case 0x8000000a: {
-- 
1.8.3.1


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