Re: [PATCH V3] perf: Add PERF_SAMPLE_PHYS_ADDR

[Stephane Eranian]

On Wed, Aug 9, 2017 at 1:42 PM,  <kan.liang@xxxxxxxxx> wrote:
> From: Kan Liang <kan.liang@xxxxxxxxx>
>
> For understanding how the workload maps to memory channels and hardware
> behavior, it's very important to collect address maps with physical
> addresses. For example, 3D XPoint access can only be found by filtering
> the physical address.
> However, perf doesn't collect physical address information in sampling.
>
> The load latency/DLA information in PEBS can be used to calculate the
> physical address.
> For kernel direct mapping addresses, virt_to_phys is used 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.
> A new sample type PERF_SAMPLE_PHYS_ADDR is introduced to expose the
> physical addresses.
>
> Signed-off-by: Kan Liang <kan.liang@xxxxxxxxx>

This is a useful feature that I would like to use for some of the
analysis we would like to do.
Please apply.
I am assuming you have the support in perf record/report?

> ---
>
> The V2 version can be found here.
> https://patchwork.kernel.org/patch/7979771/
>
> Changes since V2
>  - Only the kernel patch
>  - Add example in changelog
>  - Include a perf_paranoid_kernel() test (PeterZ)
>  - Fix minor complier warning
>
>  arch/x86/events/intel/ds.c      | 24 ++++++++++++++++++++++++
>  arch/x86/events/perf_event.h    |  2 +-
>  include/linux/perf_event.h      |  3 +++
>  include/uapi/linux/perf_event.h |  4 +++-
>  kernel/events/core.c            | 12 ++++++++++++
>  5 files changed, 43 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/events/intel/ds.c b/arch/x86/events/intel/ds.c
> index a322fed..712c86b 100644
> --- a/arch/x86/events/intel/ds.c
> +++ b/arch/x86/events/intel/ds.c
> @@ -1083,6 +1083,7 @@ 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;
> @@ -1179,6 +1180,29 @@ 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 *)(uintptr_t)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);
> +               }
> +       }
> +
This would be cleaner in a separate function in my opinion.

>         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/arch/x86/events/perf_event.h b/arch/x86/events/perf_event.h
> index 476aec3..65bb91e 100644
> --- a/arch/x86/events/perf_event.h
> +++ b/arch/x86/events/perf_event.h
> @@ -91,7 +91,7 @@ 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/include/linux/perf_event.h b/include/linux/perf_event.h
> index a3b873f..6783c69 100644
> --- a/include/linux/perf_event.h
> +++ b/include/linux/perf_event.h
> @@ -944,6 +944,8 @@ struct perf_sample_data {
>
>         struct perf_regs                regs_intr;
>         u64                             stack_user_size;
> +
> +       u64                             phys_addr;
>  } ____cacheline_aligned;
>
>  /* default value for data source */
> @@ -964,6 +966,7 @@ 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 642db5f..cbea02f 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 */
>  };
>
>  /*
> @@ -814,6 +815,7 @@ 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 426c2ff..07d4a74 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -1570,6 +1570,9 @@ 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;
>  }
>
> @@ -5952,6 +5955,9 @@ 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);
> +

I think this is misplaced. You need to output in the order in which
you describe the record in the header file.
You have: DATA_SRC, SAMPLE_TRANSACTION, REGS_INTR, PHYS_ADDR. That
means you need to
output in that order. Otherwise your PHYS_ADDR may be interpreted as a
SAMPLE_TRANSACTION in case it is active.
At least this is my understanding of the ABI here.


>         if (sample_type & PERF_SAMPLE_TRANSACTION)
>                 perf_output_put(handle, data->txn);
>
> @@ -9852,6 +9858,12 @@ SYSCALL_DEFINE5(perf_event_open,
>                         return -EINVAL;
>         }
>
> +       /* Only privileged users can get kernel addresses */
> +       if ((attr.sample_type & PERF_SAMPLE_PHYS_ADDR) &&
> +           perf_paranoid_kernel() &&
> +           !capable(CAP_SYS_ADMIN))
> +               return -EACCES;
> +
>         if (!attr.sample_max_stack)
>                 attr.sample_max_stack = sysctl_perf_event_max_stack;
>
> --
> 2.4.3
>