[PATCH v2] x86/intel: ensure Global Performance Counter Control is setup correctly

[Roger Pau Monne <roger.pau@xxxxxxxxxx>]

When Architectural Performance Monitoring is available, the PERF_GLOBAL_CTRL
MSR contains per-counter enable bits that is ANDed with the enable bit in the
counter EVNTSEL MSR in order for a PMC counter to be enabled.

So far the watchdog code seems to have relied on the PERF_GLOBAL_CTRL enable
bits being set by default, but at least on some Intel Sapphire and Emerald
Rapids this is no longer the case, and Xen reports:

Testing NMI watchdog on all CPUs: 0 40 stuck

The first CPU on each package is started with PERF_GLOBAL_CTRL zeroed, so PMC0
doesn't start counting when the enable bit in EVNTSEL0 is set, due to the
relevant enable bit in PERF_GLOBAL_CTRL not being set.

Check and adjust PERF_GLOBAL_CTRL during CPU initialization so that all the
general-purpose PMCs are enabled.  Doing so brings the state of the package-BSP
PERF_GLOBAL_CTRL in line with the rest of the CPUs on the system.

Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
---
Changes since v1:
 - Do the adjustment of PERF_GLOBAL_CTRL even if the watchdog is not used, and
   enable all counters.
---
Unsure whether printing a warning if the value of PERF_GLOBAL_CTRL is not
correct is of any value, hence I haven't added it.
---
 xen/arch/x86/cpu/intel.c | 18 +++++++++++++++++-
 1 file changed, 17 insertions(+), 1 deletion(-)

diff --git a/xen/arch/x86/cpu/intel.c b/xen/arch/x86/cpu/intel.c
index dfee64689ffe..40d3eb0e18a7 100644
--- a/xen/arch/x86/cpu/intel.c
+++ b/xen/arch/x86/cpu/intel.c
@@ -533,9 +533,25 @@ static void cf_check init_intel(struct cpuinfo_x86 *c)
        init_intel_cacheinfo(c);
        if (c->cpuid_level > 9) {
                unsigned eax = cpuid_eax(10);
+               unsigned int cnt = (uint8_t)(eax >> 8);
+
                /* Check for version and the number of counters */
-               if ((eax & 0xff) && (((eax>>8) & 0xff) > 1))
+               if ((eax & 0xff) && (cnt > 1) && (cnt <= 32)) {
+                       uint64_t global_ctrl;
+                       unsigned int cnt_mask = (1UL << cnt) - 1;
+
+                       /*
+                        * On (some?) Sapphire/Emerald Rapids platforms each
+                        * package-BSP starts with all the enable bits for the
+                        * general-purpose PMCs cleared.  Adjust so counters
+                        * can be enabled from EVNTSEL.
+                        */
+                       rdmsrl(MSR_CORE_PERF_GLOBAL_CTRL, global_ctrl);
+                       if ((global_ctrl & cnt_mask) != cnt_mask)
+                               wrmsrl(MSR_CORE_PERF_GLOBAL_CTRL,
+                                      global_ctrl | cnt_mask);
                        __set_bit(X86_FEATURE_ARCH_PERFMON, c->x86_capability);
+               }
        }
 
        if ( !cpu_has(c, X86_FEATURE_XTOPOLOGY) )
-- 
2.43.0