Re: [PATCH 1/8] perf: Add PERF_SAMPLE_PHYS_ADDR

[Stephane Eranian]

On Wed, Jan 6, 2016 at 3:04 AM,  <kan.liang@xxxxxxxxx> wrote:
> From: Kan Liang <kan.liang@xxxxxxxxx>
>
> For understanding how the workload maps to memory channels and hardware
> behavior, it's useful to collect address maps with physical addresses.
> This is not intended for detecting page sharing (which can be already
> done using the mmap inode), but for lower level hardware behavior
> studies.
> Perf supports load latency/DLA which can only collect virtual addresses.
> This patch add a new sample type PERF_SAMPLE_PHYS_ADDR to expose the
> physical addresses.
> For kernel direct mapping addresses, the patch uses virt_to_phys to
> convert the virtual addresses from DLA to physical address.
> For user virtual addresses, __get_user_pages_fast is used to walk the
> pages tables for user physical address.
> This does not work for vmalloc addresses. Right now these are not
> resolved, but code to do that could be added.
> For security, the physical address can only be exposed to root or
> privileged user.
>
The other limitation of your patch series is that it is providing
physical address for data only. It does not cover code, i.e., it is not possible
to obtain the physical address of a sampled IP. So maybe the new sample_type
should be renamed to PERF_SAMPLE_DATA_PHYS_ADDR instead.
Should you add physical addresses for IP (no need for PEBS for this), then
you'd have to have a new name, anyway.

Getting code and data physical addresses would provide better coverage
of the memory subsystem usage.

> Signed-off-by: Kan Liang <kan.liang@xxxxxxxxx>
> ---
>  arch/x86/kernel/cpu/perf_event.h          |  2 +-
>  arch/x86/kernel/cpu/perf_event_intel_ds.c | 23 +++++++++++++++++++++++
>  include/linux/perf_event.h                |  3 +++
>  include/uapi/linux/perf_event.h           |  4 +++-
>  kernel/events/core.c                      | 11 +++++++++++
>  5 files changed, 41 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/kernel/cpu/perf_event.h b/arch/x86/kernel/cpu/perf_event.h
> index 799e6bd..164de68 100644
> --- a/arch/x86/kernel/cpu/perf_event.h
> +++ b/arch/x86/kernel/cpu/perf_event.h
> @@ -90,7 +90,7 @@ struct amd_nb {
>         (PERF_SAMPLE_IP | PERF_SAMPLE_TID | PERF_SAMPLE_ADDR | \
>         PERF_SAMPLE_ID | PERF_SAMPLE_CPU | PERF_SAMPLE_STREAM_ID | \
>         PERF_SAMPLE_DATA_SRC | PERF_SAMPLE_IDENTIFIER | \
> -       PERF_SAMPLE_TRANSACTION)
> +       PERF_SAMPLE_TRANSACTION | PERF_SAMPLE_PHYS_ADDR)
>
>  /*
>   * A debug store configuration.
> diff --git a/arch/x86/kernel/cpu/perf_event_intel_ds.c b/arch/x86/kernel/cpu/perf_event_intel_ds.c
> index 5db1c77..2e333dc 100644
> --- a/arch/x86/kernel/cpu/perf_event_intel_ds.c
> +++ b/arch/x86/kernel/cpu/perf_event_intel_ds.c
> @@ -986,6 +986,7 @@ static void setup_pebs_sample_data(struct perf_event *event,
>         u64 sample_type;
>         int fll, fst, dsrc;
>         int fl = event->hw.flags;
> +       struct page *p = NULL;
>
>         if (pebs == NULL)
>                 return;
> @@ -1071,6 +1072,28 @@ static void setup_pebs_sample_data(struct perf_event *event,
>             x86_pmu.intel_cap.pebs_format >= 1)
>                 data->addr = pebs->dla;
>
> +       if ((sample_type & PERF_SAMPLE_PHYS_ADDR) && (data->addr != 0)) {
> +               if (data->addr >= TASK_SIZE) {
> +                       /* If it's vmalloc()d memory, leave phys_addr as 0 */
> +                       if (virt_addr_valid(data->addr) &&
> +                           !(data->addr >= VMALLOC_START && data->addr < VMALLOC_END))
> +                               data->phys_addr = (u64)virt_to_phys((void *)data->addr);
> +               } else {
> +                       /*
> +                        * Walking the pages tables for user address.
> +                        * Interrupts are disabled, so it prevents any tear down
> +                        * of the page tables.
> +                        * Try IRQ-safe __get_user_pages_fast first.
> +                        * If failed, leave phys_addr as 0.
> +                        */
> +                       if ((current->mm != NULL) &&
> +                           (__get_user_pages_fast(data->addr, 1, 0, &p) == 1))
> +                               data->phys_addr = page_to_phys(p) + data->addr % PAGE_SIZE;
> +
> +                       if (p)
> +                               put_page(p);
> +               }
> +       }
>         if (x86_pmu.intel_cap.pebs_format >= 2) {
>                 /* Only set the TSX weight when no memory weight. */
>                 if ((sample_type & PERF_SAMPLE_WEIGHT) && !fll)
> diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
> index f9828a4..d9c0527 100644
> --- a/include/linux/perf_event.h
> +++ b/include/linux/perf_event.h
> @@ -795,6 +795,8 @@ struct perf_sample_data {
>
>         struct perf_regs                regs_intr;
>         u64                             stack_user_size;
> +
> +       u64                             phys_addr;
>  } ____cacheline_aligned;
>
>  /* default value for data source */
> @@ -815,6 +817,7 @@ static inline void perf_sample_data_init(struct perf_sample_data *data,
>         data->weight = 0;
>         data->data_src.val = PERF_MEM_NA;
>         data->txn = 0;
> +       data->phys_addr = 0;
>  }
>
>  extern void perf_output_sample(struct perf_output_handle *handle,
> diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h
> index 1afe962..5afc572 100644
> --- a/include/uapi/linux/perf_event.h
> +++ b/include/uapi/linux/perf_event.h
> @@ -139,8 +139,9 @@ enum perf_event_sample_format {
>         PERF_SAMPLE_IDENTIFIER                  = 1U << 16,
>         PERF_SAMPLE_TRANSACTION                 = 1U << 17,
>         PERF_SAMPLE_REGS_INTR                   = 1U << 18,
> +       PERF_SAMPLE_PHYS_ADDR                   = 1U << 19,
>
> -       PERF_SAMPLE_MAX = 1U << 19,             /* non-ABI */
> +       PERF_SAMPLE_MAX = 1U << 20,             /* non-ABI */
>  };
>
>  /*
> @@ -767,6 +768,7 @@ enum perf_event_type {
>          *      { u64                   transaction; } && PERF_SAMPLE_TRANSACTION
>          *      { u64                   abi; # enum perf_sample_regs_abi
>          *        u64                   regs[weight(mask)]; } && PERF_SAMPLE_REGS_INTR
> +        *      { u64                   phys_addr;} && PERF_SAMPLE_PHYS_ADDR
>          * };
>          */
>         PERF_RECORD_SAMPLE                      = 9,
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index a627f36..9a922a2 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -1334,6 +1334,9 @@ static void __perf_event_header_size(struct perf_event *event, u64 sample_type)
>         if (sample_type & PERF_SAMPLE_TRANSACTION)
>                 size += sizeof(data->txn);
>
> +       if (sample_type & PERF_SAMPLE_PHYS_ADDR)
> +               size += sizeof(data->phys_addr);
> +
>         event->header_size = size;
>  }
>
> @@ -5432,6 +5435,9 @@ void perf_output_sample(struct perf_output_handle *handle,
>         if (sample_type & PERF_SAMPLE_DATA_SRC)
>                 perf_output_put(handle, data->data_src.val);
>
> +       if (sample_type & PERF_SAMPLE_PHYS_ADDR)
> +               perf_output_put(handle, data->phys_addr);
> +
>         if (sample_type & PERF_SAMPLE_TRANSACTION)
>                 perf_output_put(handle, data->txn);
>
> @@ -8269,6 +8275,11 @@ SYSCALL_DEFINE5(perf_event_open,
>                         return -EINVAL;
>         }
>
> +       /* Only privileged users can get kernel addresses */
> +       if ((attr.sample_type & PERF_SAMPLE_PHYS_ADDR) &&
> +           !capable(CAP_SYS_ADMIN))
> +               return -EACCES;
> +
>         /*
>          * In cgroup mode, the pid argument is used to pass the fd
>          * opened to the cgroup directory in cgroupfs. The cpu argument
> --
> 1.8.3.1
>