[PATCH] arm64/cpufeature: Move BUG_ON() inside get_arm64_ftr_reg()

[Anshuman Khandual]

There is no way to proceed when requested register could not be searched in
arm64_ftr_reg[]. Requesting for a non present register would be an error as
well. Hence lets just BUG_ON() when the search fails in get_arm64_ftr_reg()
rather than checking for return value and doing the same in some individual
callers.

But there are some callers that dont BUG_ON() upon search failure. It adds
an argument 'failsafe' that provides required switch between callers based
on whether they could proceed or not.

Cc: Catalin Marinas <catalin.mari...@arm.com>
Cc: Will Deacon <w...@kernel.org>
Cc: Suzuki K Poulose <suzuki.poul...@arm.com>
Cc: Mark Brown <broo...@kernel.org>
Cc: linux-arm-ker...@lists.infradead.org
Cc: linux-kernel@vger.kernel.org

Signed-off-by: Anshuman Khandual <anshuman.khand...@arm.com>
---
Applies on next-20200518 that has recent cpufeature changes from Will.

 arch/arm64/kernel/cpufeature.c | 26 +++++++++++++-------------
 1 file changed, 13 insertions(+), 13 deletions(-)

diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index bc5048f152c1..62767cc540c3 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -557,7 +557,7 @@ static int search_cmp_ftr_reg(const void *id, const void 
*regp)
  *         - NULL on failure. It is upto the caller to decide
  *          the impact of a failure.
  */
-static struct arm64_ftr_reg *get_arm64_ftr_reg(u32 sys_id)
+static struct arm64_ftr_reg *get_arm64_ftr_reg(u32 sys_id, bool failsafe)
 {
        const struct __ftr_reg_entry *ret;
 
@@ -568,6 +568,13 @@ static struct arm64_ftr_reg *get_arm64_ftr_reg(u32 sys_id)
                        search_cmp_ftr_reg);
        if (ret)
                return ret->reg;
+       /*
+        * This can not really proceed when the search fails.
+        * Requesting for a non existent register search will
+        * also be an error in itself. Error out when not
+        * called with fail safe request.
+        */
+       BUG_ON(!failsafe);
        return NULL;
 }
 
@@ -630,9 +637,7 @@ static void __init init_cpu_ftr_reg(u32 sys_reg, u64 new)
        u64 valid_mask = 0;
 
        const struct arm64_ftr_bits *ftrp;
-       struct arm64_ftr_reg *reg = get_arm64_ftr_reg(sys_reg);
-
-       BUG_ON(!reg);
+       struct arm64_ftr_reg *reg = get_arm64_ftr_reg(sys_reg, false);
 
        for (ftrp = reg->ftr_bits; ftrp->width; ftrp++) {
                u64 ftr_mask = arm64_ftr_mask(ftrp);
@@ -760,9 +765,8 @@ static void update_cpu_ftr_reg(struct arm64_ftr_reg *reg, 
u64 new)
 
 static int check_update_ftr_reg(u32 sys_id, int cpu, u64 val, u64 boot)
 {
-       struct arm64_ftr_reg *regp = get_arm64_ftr_reg(sys_id);
+       struct arm64_ftr_reg *regp = get_arm64_ftr_reg(sys_id, false);
 
-       BUG_ON(!regp);
        update_cpu_ftr_reg(regp, val);
        if ((boot & regp->strict_mask) == (val & regp->strict_mask))
                return 0;
@@ -774,10 +778,7 @@ static int check_update_ftr_reg(u32 sys_id, int cpu, u64 
val, u64 boot)
 static void relax_cpu_ftr_reg(u32 sys_id, int field)
 {
        const struct arm64_ftr_bits *ftrp;
-       struct arm64_ftr_reg *regp = get_arm64_ftr_reg(sys_id);
-
-       if (WARN_ON(!regp))
-               return;
+       struct arm64_ftr_reg *regp = get_arm64_ftr_reg(sys_id, false);
 
        for (ftrp = regp->ftr_bits; ftrp->width; ftrp++) {
                if (ftrp->shift == field) {
@@ -959,10 +960,9 @@ void update_cpu_features(int cpu,
 
 u64 read_sanitised_ftr_reg(u32 id)
 {
-       struct arm64_ftr_reg *regp = get_arm64_ftr_reg(id);
+       struct arm64_ftr_reg *regp = get_arm64_ftr_reg(id, false);
 
        /* We shouldn't get a request for an unsupported register */
-       BUG_ON(!regp);
        return regp->sys_val;
 }
 
@@ -2565,7 +2565,7 @@ static int emulate_sys_reg(u32 id, u64 *valp)
        if (sys_reg_CRm(id) == 0)
                return emulate_id_reg(id, valp);
 
-       regp = get_arm64_ftr_reg(id);
+       regp = get_arm64_ftr_reg(id, true);
        if (regp)
                *valp = arm64_ftr_reg_user_value(regp);
        else
-- 
2.20.1