arm64: cpufeature: Add global feature override facility

Add a facility to globally override a feature, no matter what
the HW says. Yes, this sounds dangerous, but we do respect the
"safe" value for a given feature. This doesn't mean the user
doesn't need to know what they are doing.

Nothing uses this yet, so we are pretty safe. For now.

Signed-off-by: Marc Zyngier <maz@kernel.org>
Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Acked-by: David Brazdil <dbrazdil@google.com>
Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
Link: https://lore.kernel.org/r/20210208095732.3267263-11-maz@kernel.org
Signed-off-by: Will Deacon <will@kernel.org>

diff --git a/arch/arm64/include/asm/cpufeature.h b/arch/arm64/include/asm/cpufeature.h
index 9a555809b89cdacf140af192a71cd040be66a4d2..b1f53147e2b26cf460d55bea17721131ad6b01c8 100644 (file)
--- a/arch/arm64/include/asm/cpufeature.h
+++ b/arch/arm64/include/asm/cpufeature.h
@@ -63,6 +63,11 @@ struct arm64_ftr_bits {
        s64             safe_val; /* safe value for FTR_EXACT features */
 };
 
+struct arm64_ftr_override {
+       u64             val;
+       u64             mask;
+};
+
 /*
  * @arm64_ftr_reg - Feature register
  * @strict_mask                Bits which should match across all CPUs for sanity.
@@ -74,6 +79,7 @@ struct arm64_ftr_reg {
        u64                             user_mask;
        u64                             sys_val;
        u64                             user_val;
+       struct arm64_ftr_override       *override;
        const struct arm64_ftr_bits     *ftr_bits;
 };
 

diff --git a/arch/arm64/kernel/cpufeature.c b/arch/arm64/kernel/cpufeature.c
index e99eddec0a46925b82b4f434611e2907e6747a86..a4e5c619a51642d65df6f967ca329d25fac5a73f 100644 (file)
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -352,9 +352,12 @@ static const struct arm64_ftr_bits ftr_ctr[] = {
        ARM64_FTR_END,
 };
 
+static struct arm64_ftr_override __ro_after_init no_override = { };
+
 struct arm64_ftr_reg arm64_ftr_reg_ctrel0 = {
        .name           = "SYS_CTR_EL0",
-       .ftr_bits       = ftr_ctr
+       .ftr_bits       = ftr_ctr,
+       .override       = &no_override,
 };
 
 static const struct arm64_ftr_bits ftr_id_mmfr0[] = {
@@ -544,13 +547,16 @@ static const struct arm64_ftr_bits ftr_raz[] = {
        ARM64_FTR_END,
 };
 
-#define ARM64_FTR_REG(id, table) {             \
-       .sys_id = id,                           \
-       .reg =  &(struct arm64_ftr_reg){        \
-               .name = #id,                    \
-               .ftr_bits = &((table)[0]),      \
+#define ARM64_FTR_REG_OVERRIDE(id, table, ovr) {               \
+               .sys_id = id,                                   \
+               .reg =  &(struct arm64_ftr_reg){                \
+                       .name = #id,                            \
+                       .override = (ovr),                      \
+                       .ftr_bits = &((table)[0]),              \
        }}
 
+#define ARM64_FTR_REG(id, table) ARM64_FTR_REG_OVERRIDE(id, table, &no_override)
+
 static const struct __ftr_reg_entry {
        u32                     sys_id;
        struct arm64_ftr_reg    *reg;
@@ -770,6 +776,33 @@ static void __init init_cpu_ftr_reg(u32 sys_reg, u64 new)
        for (ftrp = reg->ftr_bits; ftrp->width; ftrp++) {
                u64 ftr_mask = arm64_ftr_mask(ftrp);
                s64 ftr_new = arm64_ftr_value(ftrp, new);
+               s64 ftr_ovr = arm64_ftr_value(ftrp, reg->override->val);
+
+               if ((ftr_mask & reg->override->mask) == ftr_mask) {
+                       s64 tmp = arm64_ftr_safe_value(ftrp, ftr_ovr, ftr_new);
+                       char *str = NULL;
+
+                       if (ftr_ovr != tmp) {
+                               /* Unsafe, remove the override */
+                               reg->override->mask &= ~ftr_mask;
+                               reg->override->val &= ~ftr_mask;
+                               tmp = ftr_ovr;
+                               str = "ignoring override";
+                       } else if (ftr_new != tmp) {
+                               /* Override was valid */
+                               ftr_new = tmp;
+                               str = "forced";
+                       } else if (ftr_ovr == tmp) {
+                               /* Override was the safe value */
+                               str = "already set";
+                       }
+
+                       if (str)
+                               pr_warn("%s[%d:%d]: %s to %llx\n",
+                                       reg->name,
+                                       ftrp->shift + ftrp->width - 1,
+                                       ftrp->shift, str, tmp);
+               }
 
                val = arm64_ftr_set_value(ftrp, val, ftr_new);