Re: [PATCH v8 15/26] arm64: alternative: Apply alternatives early in boot process
From: Suzuki K Poulose
Date: Tue Jan 08 2019 - 12:40:47 EST
On 08/01/2019 15:20, Julien Thierry wrote:
Hi Suzuki,
On 08/01/2019 14:51, Suzuki K Poulose wrote:
Hi Julien,
On 08/01/2019 14:07, Julien Thierry wrote:
From: Daniel Thompson <daniel.thompson@xxxxxxxxxx>
Currently alternatives are applied very late in the boot process (and
a long time after we enable scheduling). Some alternative sequences,
such as those that alter the way CPU context is stored, must be applied
much earlier in the boot sequence.
Introduce apply_boot_alternatives() to allow some alternatives to be
applied immediately after we detect the CPU features of the boot CPU.
Signed-off-by: Daniel Thompson <daniel.thompson@xxxxxxxxxx>
[julien.thierry@xxxxxxx: rename to fit new cpufeature framework better,
ÂÂÂÂÂÂÂÂÂÂÂÂ apply BOOT_SCOPE feature early in boot]
Signed-off-by: Julien Thierry <julien.thierry@xxxxxxx>
Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
Cc: Will Deacon <will.deacon@xxxxxxx>
Cc: Christoffer Dall <christoffer.dall@xxxxxxx>
Cc: Suzuki K Poulose <suzuki.poulose@xxxxxxx>
---
 arch/arm64/include/asm/alternative.h | 1 +
 arch/arm64/include/asm/cpufeature.h | 4 ++++
 arch/arm64/kernel/alternative.c | 43
+++++++++++++++++++++++++++++++-----
 arch/arm64/kernel/cpufeature.c | 6 +++++
 arch/arm64/kernel/smp.c | 7 ++++++
 5 files changed, 56 insertions(+), 5 deletions(-)
diff --git a/arch/arm64/include/asm/alternative.h
b/arch/arm64/include/asm/alternative.h
index 9806a23..b9f8d78 100644
--- a/arch/arm64/include/asm/alternative.h
+++ b/arch/arm64/include/asm/alternative.h
@@ -25,6 +25,7 @@ struct alt_instr {
 typedef void (*alternative_cb_t)(struct alt_instr *alt,
ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ __le32 *origptr, __le32 *updptr, int nr_inst);
 +void __init apply_boot_alternatives(void);
 void __init apply_alternatives_all(void);
 bool alternative_is_applied(u16 cpufeature);
 diff --git a/arch/arm64/include/asm/cpufeature.h
b/arch/arm64/include/asm/cpufeature.h
index 89c3f31..e505e1f 100644
--- a/arch/arm64/include/asm/cpufeature.h
+++ b/arch/arm64/include/asm/cpufeature.h
@@ -391,6 +391,10 @@ static inline int cpucap_default_scope(const
struct arm64_cpu_capabilities *cap)
 extern struct static_key_false cpu_hwcap_keys[ARM64_NCAPS];
 extern struct static_key_false arm64_const_caps_ready;
 +/* ARM64 CAPS + alternative_cb */
+#define ARM64_NPATCHABLE (ARM64_NCAPS + 1)
+extern DECLARE_BITMAP(boot_capabilities, ARM64_NPATCHABLE);
+
 #define for_each_available_cap(cap) \
ÂÂÂÂÂ for_each_set_bit(cap, cpu_hwcaps, ARM64_NCAPS)
 diff --git a/arch/arm64/kernel/alternative.c
b/arch/arm64/kernel/alternative.c
index c947d22..a9b4677 100644
--- a/arch/arm64/kernel/alternative.c
+++ b/arch/arm64/kernel/alternative.c
@@ -155,7 +155,8 @@ static void clean_dcache_range_nopatch(u64 start,
u64 end)
ÂÂÂÂÂ } while (cur += d_size, cur < end);
 }
 -static void __apply_alternatives(void *alt_region, bool is_module)
+static void __apply_alternatives(void *alt_region, bool is_module,
+ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ unsigned long *feature_mask)
 {
ÂÂÂÂÂ struct alt_instr *alt;
ÂÂÂÂÂ struct alt_region *region = alt_region;
@@ -165,6 +166,9 @@ static void __apply_alternatives(void *alt_region,
bool is_module)
ÂÂÂÂÂ for (alt = region->begin; alt < region->end; alt++) {
ÂÂÂÂÂÂÂÂÂ int nr_inst;
 + if (!test_bit(alt->cpufeature, feature_mask))
+ÂÂÂÂÂÂÂÂÂÂÂ continue;
+
ÂÂÂÂÂÂÂÂÂ /* Use ARM64_CB_PATCH as an unconditional patch */
ÂÂÂÂÂÂÂÂÂ if (alt->cpufeature < ARM64_CB_PATCH &&
ÂÂÂÂÂÂÂÂÂÂÂÂÂ !cpus_have_cap(alt->cpufeature))
@@ -203,8 +207,11 @@ static void __apply_alternatives(void
*alt_region, bool is_module)
ÂÂÂÂÂÂÂÂÂ __flush_icache_all();
ÂÂÂÂÂÂÂÂÂ isb();
 - /* We applied all that was available */
-ÂÂÂÂÂÂÂ bitmap_copy(applied_alternatives, cpu_hwcaps, ARM64_NCAPS);
+ÂÂÂÂÂÂÂ /* Ignore ARM64_CB bit from feature mask */
+ÂÂÂÂÂÂÂ bitmap_or(applied_alternatives, applied_alternatives,
+ÂÂÂÂÂÂÂÂÂÂÂÂÂ feature_mask, ARM64_NCAPS);
+ÂÂÂÂÂÂÂ bitmap_and(applied_alternatives, applied_alternatives,
+ÂÂÂÂÂÂÂÂÂÂÂÂÂÂ cpu_hwcaps, ARM64_NCAPS);
ÂÂÂÂÂ }
 }
 @@ -225,8 +232,13 @@ static int __apply_alternatives_multi_stop(void
*unused)
ÂÂÂÂÂÂÂÂÂÂÂÂÂ cpu_relax();
ÂÂÂÂÂÂÂÂÂ isb();
ÂÂÂÂÂ } else {
+ÂÂÂÂÂÂÂ DECLARE_BITMAP(remaining_capabilities, ARM64_NPATCHABLE);
+
+ÂÂÂÂÂÂÂ bitmap_complement(remaining_capabilities, boot_capabilities,
+ÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂÂ ARM64_NPATCHABLE);
+
ÂÂÂÂÂÂÂÂÂ BUG_ON(all_alternatives_applied);
-ÂÂÂÂÂÂÂ __apply_alternatives(®ion, false);
+ÂÂÂÂÂÂÂ __apply_alternatives(®ion, false, remaining_capabilities);
ÂÂÂÂÂÂÂÂÂ /* Barriers provided by the cache flushing */
ÂÂÂÂÂÂÂÂÂ WRITE_ONCE(all_alternatives_applied, 1);
ÂÂÂÂÂ }
@@ -240,6 +252,24 @@ void __init apply_alternatives_all(void)
ÂÂÂÂÂ stop_machine(__apply_alternatives_multi_stop, NULL,
cpu_online_mask);
 }
 +/*
+ * This is called very early in the boot process (directly after we run
+ * a feature detect on the boot CPU). No need to worry about other CPUs
+ * here.
+ */
+void __init apply_boot_alternatives(void)
+{
+ÂÂÂ struct alt_region region = {
+ÂÂÂÂÂÂÂ .beginÂÂÂ = (struct alt_instr *)__alt_instructions,
+ÂÂÂÂÂÂÂ .endÂÂÂ = (struct alt_instr *)__alt_instructions_end,
+ÂÂÂ };
+
+ÂÂÂ /* If called on non-boot cpu things could go wrong */
+ÂÂÂ WARN_ON(smp_processor_id() != 0);
+
+ÂÂÂ __apply_alternatives(®ion, false, &boot_capabilities[0]);
+}
+
 #ifdef CONFIG_MODULES
 void apply_alternatives_module(void *start, size_t length)
 {
@@ -247,7 +277,10 @@ void apply_alternatives_module(void *start,
size_t length)
ÂÂÂÂÂÂÂÂÂ .beginÂÂÂ = start,
ÂÂÂÂÂÂÂÂÂ .endÂÂÂ = start + length,
ÂÂÂÂÂ };
+ÂÂÂ DECLARE_BITMAP(all_capabilities, ARM64_NPATCHABLE);
+
+ÂÂÂ bitmap_fill(all_capabilities, ARM64_NPATCHABLE);
 - __apply_alternatives(®ion, true);
+ÂÂÂ __apply_alternatives(®ion, true, &all_capabilities[0]);
 }
 #endif
diff --git a/arch/arm64/kernel/cpufeature.c
b/arch/arm64/kernel/cpufeature.c
index 84fa5be..71c8d4f 100644
--- a/arch/arm64/kernel/cpufeature.c
+++ b/arch/arm64/kernel/cpufeature.c
@@ -54,6 +54,9 @@
 EXPORT_SYMBOL(cpu_hwcaps);
 static struct arm64_cpu_capabilities const __ro_after_init
*cpu_hwcaps_ptrs[ARM64_NCAPS];
 +/* Need also bit for ARM64_CB_PATCH */
+DECLARE_BITMAP(boot_capabilities, ARM64_NPATCHABLE);
+
 /*
ÂÂ * Flag to indicate if we have computed the system wide
ÂÂ * capabilities based on the boot time active CPUs. This
@@ -1672,6 +1675,9 @@ static void update_cpu_capabilities(u16 scope_mask)
ÂÂÂÂÂÂÂÂÂ if (caps->desc)
ÂÂÂÂÂÂÂÂÂÂÂÂÂ pr_info("detected: %s\n", caps->desc);
ÂÂÂÂÂÂÂÂÂ cpus_set_cap(caps->capability);
+
+ÂÂÂÂÂÂÂ if (caps->type & SCOPE_BOOT_CPU)
You may want to do :
ÂÂÂÂÂÂÂ if (scope_mask & SCOPE_BOOT_CPU)
for a tighter check to ensure this doesn't update the boot_capabilities
after we have applied the boot_scope alternatives and miss applying the
alternatives for those, should someone add a multi-scope (i.e
SCOPE_BOOT_CPU and
something else) capability (even by mistake).
But a multi-scope capability containing SCOPE_BOOT_CPU should already
get updated for setup_boot_cpu_capabilities. Capabilities marked with
SCOPE_BOOT_CPU need to be enabled on the boot CPU or not at all.
Yes, you're right. It is not normal to have multiple SCOPE for a "capability".
But if someone comes with such a cap, we may miss handling this case. It is
always better to be safer.
Shouldn't the call to caps->matches() fail for a boot feature that was
not found on the boot cpu?
Also, you made the opposite suggestion 4 version ago with a more
worrying scenario :) :
https://lkml.org/lkml/2018/5/25/208
Ah, you're right. I missed that. We need the additional check as you mention
below.
Otherwise, if my assumption above is wrong, it means the check should
probably be:
if (caps->type & SCOPE_BOOT_CPU && scope_mask & SCOPE_BOOT_CPU)
Yes, this is what we want.
But my current understanding is that we don't need that.
With that:
Reviewed-by: Suzuki K Poulose <suzuki.poulose@xxxxxxx>
Cheers
Suzuki