linux-kernel - [PATCH v4 2/3] cacheinfo: Add arm64 early level initializer implementation

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Message-Id: <20230412185759.755408-3-rrendec@redhat.com>
Date:   Wed, 12 Apr 2023 14:57:58 -0400
From:   Radu Rendec <rrendec@...hat.com>
To:     linux-kernel@...r.kernel.org
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Pierre Gondois <Pierre.Gondois@....com>,
        Sudeep Holla <sudeep.holla@....com>,
        linux-arm-kernel@...ts.infradead.org
Subject: [PATCH v4 2/3] cacheinfo: Add arm64 early level initializer implementation

This patch adds an architecture specific early cache level detection
handler for arm64. This is basically the CLIDR_EL1 based detection that
was previously done (only) in init_cache_level().

This is part of a patch series that attempts to further the work in
commit 5944ce092b97 ("arch_topology: Build cacheinfo from primary CPU").
Previously, in the absence of any DT/ACPI cache info, architecture
specific cache detection and info allocation for secondary CPUs would
happen in non-preemptible context during early CPU initialization and
trigger a "BUG: sleeping function called from invalid context" splat on
an RT kernel.

This patch does not solve the problem completely for RT kernels. It
relies on the assumption that on most systems, the CPUs are symmetrical
and therefore have the same number of cache leaves. The cacheinfo memory
is allocated early (on the primary CPU), relying on the new handler. If
later (when CLIDR_EL1 based detection runs again on the secondary CPU)
the initial assumption proves to be wrong and the CPU has in fact more
leaves, the cacheinfo memory is reallocated, and that still triggers a
splat on an RT kernel.

In other words, asymmetrical CPU systems *must* still provide cacheinfo
data in DT/ACPI to avoid the splat on RT kernels (unless secondary CPUs
happen to have less leaves than the primary CPU). But symmetrical CPU
systems (the majority) can now get away without the additional DT/ACPI
data and rely on CLIDR_EL1 based detection.

Signed-off-by: Radu Rendec <rrendec@...hat.com>
Reviewed-by: Pierre Gondois <pierre.gondois@....com>
---
 arch/arm64/kernel/cacheinfo.c | 25 ++++++++++++++++++++++---
 1 file changed, 22 insertions(+), 3 deletions(-)

diff --git a/arch/arm64/kernel/cacheinfo.c b/arch/arm64/kernel/cacheinfo.c
index c307f69e9b55..d9c9218fa1fd 100644
--- a/arch/arm64/kernel/cacheinfo.c
+++ b/arch/arm64/kernel/cacheinfo.c
@@ -38,11 +38,9 @@ static void ci_leaf_init(struct cacheinfo *this_leaf,
 	this_leaf->type = type;
 }

-int init_cache_level(unsigned int cpu)
+static void detect_cache_level(unsigned int *level_p, unsigned int *leaves_p)
 {
 	unsigned int ctype, level, leaves;
-	int fw_level, ret;
-	struct cpu_cacheinfo *this_cpu_ci = get_cpu_cacheinfo(cpu);

 	for (level = 1, leaves = 0; level <= MAX_CACHE_LEVEL; level++) {
 		ctype = get_cache_type(level);
@@ -54,6 +52,27 @@ int init_cache_level(unsigned int cpu)
 		leaves += (ctype == CACHE_TYPE_SEPARATE) ? 2 : 1;
 	}

+	*level_p = level;
+	*leaves_p = leaves;
+}
+
+int early_cache_level(unsigned int cpu)
+{
+	struct cpu_cacheinfo *this_cpu_ci = get_cpu_cacheinfo(cpu);
+
+	detect_cache_level(&this_cpu_ci->num_levels, &this_cpu_ci->num_leaves);
+
+	return 0;
+}
+
+int init_cache_level(unsigned int cpu)
+{
+	unsigned int level, leaves;
+	int fw_level, ret;
+	struct cpu_cacheinfo *this_cpu_ci = get_cpu_cacheinfo(cpu);
+
+	detect_cache_level(&level, &leaves);
+
 	if (acpi_disabled) {
 		fw_level = of_find_last_cache_level(cpu);
 	} else {
-- 
2.39.2