Re: [PATCH V6] perf: Add PERF_SAMPLE_PHYS_ADDR

From: Peter Zijlstra
Date: Wed Aug 23 2017 - 10:33:23 EST


Michael, Maddy,

Since PPC implements PERF_SAMPLE_ADDR this affects you guys too, please
have a look.

On Wed, Aug 23, 2017 at 10:22:46AM -0400, 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 virtual address which stored in data->addr can be used to calculate
> the physical address.
> For kernel direct mapping addresses, virt_to_phys is used to convert the
> virtual addresses 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.

Please reflow that..

> Signed-off-by: Kan Liang <kan.liang@xxxxxxxxx>
> ---
>
> This patch is kernel patch.
> The user space patch can be found here.
> https://www.spinics.net/lists/kernel/msg2587093.html
>
> Changes since V5
> - Move virt_to_phys to generic code (PeterZ)
>
> arch/x86/events/perf_event.h | 2 +-
> include/linux/perf_event.h | 2 ++
> include/uapi/linux/perf_event.h | 4 +++-
> kernel/events/core.c | 47 +++++++++++++++++++++++++++++++++++++++++
> 4 files changed, 53 insertions(+), 2 deletions(-)
>
> 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 b14095b..74fb87e 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 */
> 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 d704e23..b991af3 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;
> }
>
> @@ -6012,6 +6015,9 @@ void perf_output_sample(struct perf_output_handle *handle,
> }
> }
>
> + if (sample_type & PERF_SAMPLE_PHYS_ADDR)
> + perf_output_put(handle, data->phys_addr);
> +
> if (!event->attr.watermark) {
> int wakeup_events = event->attr.wakeup_events;
>
> @@ -6027,6 +6033,38 @@ void perf_output_sample(struct perf_output_handle *handle,
> }
> }
>
> +static u64 perf_virt_to_phys(u64 virt)
> +{
> + u64 phys_addr = 0;
> + struct page *p = NULL;
> +
> + if (!virt)
> + return 0;
> +
> + if (virt >= TASK_SIZE) {
> + /* If it's vmalloc()d memory, leave phys_addr as 0 */
> + if (virt_addr_valid(virt) &&
> + !(virt >= VMALLOC_START && virt < VMALLOC_END))
> + phys_addr = (u64)virt_to_phys((void *)(uintptr_t)virt);
> + } 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(virt, 1, 0, &p) == 1))
> + phys_addr = page_to_phys(p) + virt % PAGE_SIZE;
> +
> + if (p)
> + put_page(p);
> + }
> +
> + return phys_addr;
> +}

Michael, does this work for PPC as is?

> +
> void perf_prepare_sample(struct perf_event_header *header,
> struct perf_sample_data *data,
> struct perf_event *event,
> @@ -6145,6 +6183,9 @@ void perf_prepare_sample(struct perf_event_header *header,
>
> header->size += size;
> }
> +
> + if (sample_type & PERF_SAMPLE_PHYS_ADDR)
> + data->phys_addr = perf_virt_to_phys(data->addr);

Only problem with this now is that it requires SAMPLE_ADDR to also be
set in order to obtain data->addr.

Either fix all to set data->attr for (SAMPLE_ADDR || SAMPLE_PHYS_ADDR)
or mandate SAMPLE_ADDR when SAMPLE_PHYS_ADDR.

> }
>
> static void __always_inline
> @@ -9892,6 +9933,12 @@ 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
>