[Xen-changelog] [xen staging] x86/AMD: make use of CPUID leaf 0xb when available

[patchbot@xxxxxxx]

commit 082f070c063e2f4e215388fa3f803ec947c999cb
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Tue Jun 11 17:21:34 2019 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Tue Jun 11 17:21:34 2019 +0200

    x86/AMD: make use of CPUID leaf 0xb when available
    
    Initially I did simply stumble across a backport of Linux commit
    e0ceeae708 ("x86/CPU/hygon: Fix phys_proc_id calculation logic for
    multi-die processors") to our kernels. There I got puzzled by the claim
    that a similar change isn't needed on the AMD side. As per the web page
    cited [1], there aren't supposed to be affected AMD processors, but
    according to my reading there are: The EPYC 7000 series comes with 8,
    16, 24, or 32 cores, which I imply to be 1, 2, 3, or 4 die processors.
    And many of them have "1P/2P" in the "socket count" column. Therefore
    our calculation, being based on CPUID.80000008.EBX[15:12], would be
    similarly wrong on such 2-socket 1- or 2-die systems.
    
    Checking Linux code I then found that they don't even rely on the
    calculation we currently use anymore, at least not in the case when
    leaf 0xb is available (which is the case on Fam17). Let's follow
    Suravee's Linux commit 3986a0a805 ("x86/CPU/AMD: Derive CPU topology
    from CPUID function 0xB when available") in this regard to address this.
    
    To avoid logging duplicate information, make the function return bool.
    Move its and detect_ht()'s declaration to a private header at the same
    time.
    
    [1] https://www.amd.com/en/products/specifications/processors
    
    Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
    Acked-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
 xen/arch/x86/cpu/amd.c          | 7 +++++++
 xen/arch/x86/cpu/common.c       | 8 +++++---
 xen/arch/x86/cpu/cpu.h          | 3 +++
 xen/include/asm-x86/processor.h | 4 ----
 4 files changed, 15 insertions(+), 7 deletions(-)

diff --git a/xen/arch/x86/cpu/amd.c b/xen/arch/x86/cpu/amd.c
index 8404cf290f..e8be2e6c50 100644
--- a/xen/arch/x86/cpu/amd.c
+++ b/xen/arch/x86/cpu/amd.c
@@ -515,6 +515,13 @@ static void amd_get_topology(struct cpuinfo_x86 *c)
                         c->cpu_core_id = ebx & 0xFF;
                         c->x86_max_cores /= c->x86_num_siblings;
                 }
+
+                /*
+                 * In case leaf B is available, use it to derive
+                 * topology information.
+                 */
+                if (detect_extended_topology(c))
+                        return;
         }
         
         if (opt_cpu_info)
diff --git a/xen/arch/x86/cpu/common.c b/xen/arch/x86/cpu/common.c
index 4985a4a0ae..1db96d959c 100644
--- a/xen/arch/x86/cpu/common.c
+++ b/xen/arch/x86/cpu/common.c
@@ -533,7 +533,7 @@ void identify_cpu(struct cpuinfo_x86 *c)
  * Check for extended topology enumeration cpuid leaf 0xb and if it
  * exists, use it for cpu topology detection.
  */
-void detect_extended_topology(struct cpuinfo_x86 *c)
+bool detect_extended_topology(struct cpuinfo_x86 *c)
 {
        unsigned int eax, ebx, ecx, edx, sub_index;
        unsigned int ht_mask_width, core_plus_mask_width;
@@ -541,13 +541,13 @@ void detect_extended_topology(struct cpuinfo_x86 *c)
        unsigned int initial_apicid;
 
        if ( c->cpuid_level < 0xb )
-               return;
+               return false;
 
        cpuid_count(0xb, SMT_LEVEL, &eax, &ebx, &ecx, &edx);
 
        /* Check if the cpuid leaf 0xb is actually implemented */
        if ( ebx == 0 || (LEAFB_SUBTYPE(ecx) != SMT_TYPE) )
-               return;
+               return false;
 
        __set_bit(X86_FEATURE_XTOPOLOGY, c->x86_capability);
 
@@ -588,6 +588,8 @@ void detect_extended_topology(struct cpuinfo_x86 *c)
                        printk("CPU: Processor Core ID: %d\n",
                               c->cpu_core_id);
        }
+
+       return true;
 }
 
 void detect_ht(struct cpuinfo_x86 *c)
diff --git a/xen/arch/x86/cpu/cpu.h b/xen/arch/x86/cpu/cpu.h
index 30cd3a8578..c2f4d9a06a 100644
--- a/xen/arch/x86/cpu/cpu.h
+++ b/xen/arch/x86/cpu/cpu.h
@@ -15,4 +15,7 @@ extern unsigned int opt_cpuid_mask_ext_ecx, 
opt_cpuid_mask_ext_edx;
 extern int get_model_name(struct cpuinfo_x86 *c);
 extern void display_cacheinfo(struct cpuinfo_x86 *c);
 
+extern void detect_ht(struct cpuinfo_x86 *c);
+extern bool detect_extended_topology(struct cpuinfo_x86 *c);
+
 void early_init_amd(struct cpuinfo_x86 *c);
diff --git a/xen/include/asm-x86/processor.h b/xen/include/asm-x86/processor.h
index cef3ffb8b0..6051b92fdb 100644
--- a/xen/include/asm-x86/processor.h
+++ b/xen/include/asm-x86/processor.h
@@ -170,10 +170,6 @@ extern void setup_force_cpu_cap(unsigned int);
 extern void print_cpu_info(unsigned int cpu);
 extern unsigned int init_intel_cacheinfo(struct cpuinfo_x86 *c);
 
-extern void detect_extended_topology(struct cpuinfo_x86 *c);
-
-extern void detect_ht(struct cpuinfo_x86 *c);
-
 #define cpu_to_core(_cpu)   (cpu_data[_cpu].cpu_core_id)
 #define cpu_to_socket(_cpu) (cpu_data[_cpu].phys_proc_id)
 
--
generated by git-patchbot for /home/xen/git/xen.git#staging

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