Re: [PATCH v2 01/23] kcsan: Refactor reading of instrumented memory

Mark Rutland
2021-11-18T11:08:54Z

On Thu, Nov 18, 2021 at 09:10:05AM +0100, Marco Elver wrote:
> Factor out the switch statement reading instrumented memory into a
> helper read_instrumented_memory().
>
> No functional change.
>
> Signed-off-by: Marco Elver <elver@google.com>

Nice cleanup!

Acked-by: Mark Rutland <mark.rutland@arm.com>

Mark.

> ---
> kernel/kcsan/core.c | 51 +++++++++++++++------------------------------
> 1 file changed, 17 insertions(+), 34 deletions(-)
>
> diff --git a/kernel/kcsan/core.c b/kernel/kcsan/core.c
> index 4b84c8e7884b..6bfd3040f46b 100644
> --- a/kernel/kcsan/core.c
> +++ b/kernel/kcsan/core.c
> @@ -325,6 +325,21 @@ static void delay_access(int type)
> udelay(delay);
> }
>
> +/*
> + * Reads the instrumented memory for value change detection; value change
> + * detection is currently done for accesses up to a size of 8 bytes.
> + */
> +static __always_inline u64 read_instrumented_memory(const volatile void *ptr, size_t size)
> +{
> + switch (size) {
> + case 1: return READ_ONCE(*(const u8 *)ptr);
> + case 2: return READ_ONCE(*(const u16 *)ptr);
> + case 4: return READ_ONCE(*(const u32 *)ptr);
> + case 8: return READ_ONCE(*(const u64 *)ptr);
> + default: return 0; /* Ignore; we do not diff the values. */
> + }
> +}
> +
> void kcsan_save_irqtrace(struct task_struct *task)
> {
> #ifdef CONFIG_TRACE_IRQFLAGS
> @@ -482,23 +497,7 @@ kcsan_setup_watchpoint(const volatile void *ptr, size_t size, int type, unsigned
> * Read the current value, to later check and infer a race if the data
> * was modified via a non-instrumented access, e.g. from a device.
> */
> - old = 0;
> - switch (size) {
> - case 1:
> - old = READ_ONCE(*(const u8 *)ptr);
> - break;
> - case 2:
> - old = READ_ONCE(*(const u16 *)ptr);
> - break;
> - case 4:
> - old = READ_ONCE(*(const u32 *)ptr);
> - break;
> - case 8:
> - old = READ_ONCE(*(const u64 *)ptr);
> - break;
> - default:
> - break; /* ignore; we do not diff the values */
> - }
> + old = read_instrumented_memory(ptr, size);
>
> /*
> * Delay this thread, to increase probability of observing a racy
> @@ -511,23 +510,7 @@ kcsan_setup_watchpoint(const volatile void *ptr, size_t size, int type, unsigned
> * racy access.
> */
> access_mask = ctx->access_mask;
> - new = 0;
> - switch (size) {
> - case 1:
> - new = READ_ONCE(*(const u8 *)ptr);
> - break;
> - case 2:
> - new = READ_ONCE(*(const u16 *)ptr);
> - break;
> - case 4:
> - new = READ_ONCE(*(const u32 *)ptr);
> - break;
> - case 8:
> - new = READ_ONCE(*(const u64 *)ptr);
> - break;
> - default:
> - break; /* ignore; we do not diff the values */
> - }
> + new = read_instrumented_memory(ptr, size);
>
> diff = old ^ new;
> if (access_mask)
> --
> 2.34.0.rc2.393.gf8c9666880-goog
>