[PATCH V2] perf/x86/intel/uncore: Querying number of CHAs from CAPID6 register

[kan . liang]

From: Kan Liang <kan.liang@xxxxxxxxxxxxxxx>

The number of CHAs is miscalculated on multi PCI domain systems on
Skylake server.

(From Kroening, Gary:

For systems with a single PCI segment, it is sufficient to look for the
bus number to change in order to determine that all of the CHa's have
been counted for a single socket.
However, for multi PCI segment systems, each socket is given a new
segment and the bus number does NOT change.  So looking only for the
bus number to change ends up counting all of the CHa's on all sockets
in the system.  This leads to writing CPU MSRs beyond a valid range and
causes an error in ivbep_uncore_msr_init_box().)

To determine the number of CHAs, it should read bits 27:0 in the CAPID6
register located at Device 30, Function 3, Offset 0x9C. These 28 bits
form a bit vector of available LLC slices and the CHAs that manage those
slices.

Fixes: cd34cd97b7b4 ("perf/x86/intel/uncore: Add Skylake server uncore
support")
Reported-by: Kroening, Gary <gary.kroening@xxxxxxx>
Signed-off-by: Kan Liang <kan.liang@xxxxxxxxxxxxxxx>
---

Changes since V1:
 - add missed pci_dev_put()
 - Drop ugly casting by using hweight32()
 - Add comments for macros.

 arch/x86/events/intel/uncore_snbep.c | 31 +++++++++++++++++--------------
 1 file changed, 17 insertions(+), 14 deletions(-)

diff --git a/arch/x86/events/intel/uncore_snbep.c b/arch/x86/events/intel/uncore_snbep.c
index 6d8044a..8970f71 100644
--- a/arch/x86/events/intel/uncore_snbep.c
+++ b/arch/x86/events/intel/uncore_snbep.c
@@ -3562,24 +3562,27 @@ static struct intel_uncore_type *skx_msr_uncores[] = {
 	NULL,
 };
 
+/*
+ * To determine the number of CHAs, it should read bits 27:0 in the CAPID6
+ * register which located at Device 30, Function 3, Offset 0x9C. PCI ID 0x2083.
+ */
+#define SKX_CAPID6		0x9c
+#define SKX_CHA_BIT_MASK	GENMASK(27, 0)
+
 static int skx_count_chabox(void)
 {
-	struct pci_dev *chabox_dev = NULL;
-	int bus, count = 0;
+	struct pci_dev *dev = NULL;
+	u32 val = 0;
 
-	while (1) {
-		chabox_dev = pci_get_device(PCI_VENDOR_ID_INTEL, 0x208d, chabox_dev);
-		if (!chabox_dev)
-			break;
-		if (count == 0)
-			bus = chabox_dev->bus->number;
-		if (bus != chabox_dev->bus->number)
-			break;
-		count++;
-	}
+	dev = pci_get_device(PCI_VENDOR_ID_INTEL, 0x2083, dev);
+	if (!dev)
+		goto out;
 
-	pci_dev_put(chabox_dev);
-	return count;
+	pci_read_config_dword(dev, SKX_CAPID6, &val);
+	val &= SKX_CHA_BIT_MASK;
+out:
+	pci_dev_put(dev);
+	return hweight32(val);
 }
 
 void skx_uncore_cpu_init(void)
-- 
2.7.4