arm64/boot: Disable trapping of PMZR_EL0 writes to EL2grafted

__init_el2_fgt2() writes one mask to both HDFGRTR2_EL2 and HDFGWTR2_EL2.
PMZR_EL0 is write-only, so its trap bit, nPMZR_EL0, exists only in
HDFGWTR2_EL2 and is therefore never set: a PMZR_EL0 write from the host
traps to EL2, where the nVHE hypervisor has no handler and BUG()s. The
kernel never writes PMZR_EL0, but kernel.perf_user_access=1 has the PMU
driver set PMUSERENR_EL0.UEN for a task with a user-read event, so a
write from EL0 reaches the trap and takes the host down without a panic
message.

Accumulate the HDFGWTR2_EL2 bits separately, as __init_el2_fgt() already
does for HDFGWTR_EL2, and set nPMZR_EL0 with the other FEAT_PMUv3p9
bits.

Fixes: 858c7bfcb35e1 ("arm64/boot: Enable EL2 requirements for FEAT_PMUv3p9")
Cc: stable@vger.kernel.org
Signed-off-by: Fuad Tabba <fuad.tabba@linux.dev>
Reviewed-by: Anshuman Khandual <anshuman.khandual@arm.com>
Reviewed-by: Oliver Upton <oupton@kernel.org>
Signed-off-by: Will Deacon <will@kernel.org>

1 files changed, 55 insertions, 0 deletions

diff --git a/Documentation/admin-guide/numastat.rst b/Documentation/admin-guide/numastat.rst
new file mode 100644
index 000000000..08ec2c2bd
--- /dev/null
+++ b/Documentation/admin-guide/numastat.rst
@@ -0,0 +1,55 @@
+===============================
+Numa policy hit/miss statistics
+===============================
+
+/sys/devices/system/node/node*/numastat
+
+All units are pages. Hugepages have separate counters.
+
+The numa_hit, numa_miss and numa_foreign counters reflect how well processes
+are able to allocate memory from nodes they prefer. If they succeed, numa_hit
+is incremented on the preferred node, otherwise numa_foreign is incremented on
+the preferred node and numa_miss on the node where allocation succeeded.
+
+Usually preferred node is the one local to the CPU where the process executes,
+but restrictions such as mempolicies can change that, so there are also two
+counters based on CPU local node. local_node is similar to numa_hit and is
+incremented on allocation from a node by CPU on the same node. other_node is
+similar to numa_miss and is incremented on the node where allocation succeeds
+from a CPU from a different node. Note there is no counter analogical to
+numa_foreign.
+
+In more detail:
+
+=============== ============================================================
+numa_hit	A process wanted to allocate memory from this node,
+		and succeeded.
+
+numa_miss	A process wanted to allocate memory from another node,
+		but ended up with memory from this node.
+
+numa_foreign	A process wanted to allocate on this node,
+		but ended up with memory from another node.
+
+local_node	A process ran on this node's CPU,
+		and got memory from this node.
+
+other_node	A process ran on a different node's CPU
+		and got memory from this node.
+
+interleave_hit 	Interleaving wanted to allocate from this node
+		and succeeded.
+=============== ============================================================
+
+For easier reading you can use the numastat utility from the numactl package
+(http://oss.sgi.com/projects/libnuma/). Note that it only works
+well right now on machines with a small number of CPUs.
+
+Note that on systems with memoryless nodes (where a node has CPUs but no
+memory) the numa_hit, numa_miss and numa_foreign statistics can be skewed
+heavily. In the current kernel implementation, if a process prefers a
+memoryless node (i.e.  because it is running on one of its local CPU), the
+implementation actually treats one of the nearest nodes with memory as the
+preferred node. As a result, such allocation will not increase the numa_foreign
+counter on the memoryless node, and will skew the numa_hit, numa_miss and
+numa_foreign statistics of the nearest node.