| lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
|
Open Source and information security mailing list archives
| ||
|
Message-ID: <ZIikv0bW1xGeLf6B@FVFF77S0Q05N.cambridge.arm.com>
Date: Tue, 13 Jun 2023 18:17:51 +0100
From: Mark Rutland <mark.rutland@....com>
To: Anshuman Khandual <anshuman.khandual@....com>
Cc: linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
will@...nel.org, catalin.marinas@....com,
Mark Brown <broonie@...nel.org>,
James Clark <james.clark@....com>,
Rob Herring <robh@...nel.org>, Marc Zyngier <maz@...nel.org>,
Suzuki Poulose <suzuki.poulose@....com>,
Peter Zijlstra <peterz@...radead.org>,
Ingo Molnar <mingo@...hat.com>,
Arnaldo Carvalho de Melo <acme@...nel.org>,
linux-perf-users@...r.kernel.org
Subject: Re: [PATCH V11 08/10] arm64/perf: Add struct brbe_regset helper
functions
On Wed, May 31, 2023 at 09:34:26AM +0530, Anshuman Khandual wrote:
> The primary abstraction level for fetching branch records from BRBE HW has
> been changed as 'struct brbe_regset', which contains storage for all three
> BRBE registers i.e BRBSRC, BRBTGT, BRBINF. Whether branch record processing
> happens in the task sched out path, or in the PMU IRQ handling path, these
> registers need to be extracted from the HW. Afterwards both live and stored
> sets need to be stitched together to create final branch records set. This
> adds required helper functions for such operations.
>
> Cc: Catalin Marinas <catalin.marinas@....com>
> Cc: Will Deacon <will@...nel.org>
> Cc: Mark Rutland <mark.rutland@....com>
> Cc: linux-arm-kernel@...ts.infradead.org
> Cc: linux-kernel@...r.kernel.org
> Tested-by: James Clark <james.clark@....com>
> Signed-off-by: Anshuman Khandual <anshuman.khandual@....com>
> ---
> drivers/perf/arm_brbe.c | 163 ++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 163 insertions(+)
>
> diff --git a/drivers/perf/arm_brbe.c b/drivers/perf/arm_brbe.c
> index 484842d8cf3e..759db681d673 100644
> --- a/drivers/perf/arm_brbe.c
> +++ b/drivers/perf/arm_brbe.c
> @@ -44,6 +44,169 @@ static void select_brbe_bank(int bank)
> isb();
> }
>
> +/*
> + * This scans over BRBE register banks and captures individual branch reocrds
> + * [BRBSRC, BRBTGT, BRBINF] into a pre-allocated 'struct brbe_regset' buffer,
> + * until an invalid one gets encountered. The caller for this function needs
> + * to ensure BRBE is an appropriate state before the records can be captured.
> + */
> +static int capture_brbe_regset(struct brbe_hw_attr *brbe_attr, struct brbe_regset *buf)
> +{
> + int loop1_idx1, loop1_idx2, loop2_idx1, loop2_idx2;
> + int idx, count;
> +
> + loop1_idx1 = BRBE_BANK0_IDX_MIN;
> + if (brbe_attr->brbe_nr <= BRBE_BANK_MAX_ENTRIES) {
> + loop1_idx2 = brbe_attr->brbe_nr - 1;
> + loop2_idx1 = BRBE_BANK1_IDX_MIN;
> + loop2_idx2 = BRBE_BANK0_IDX_MAX;
> + } else {
> + loop1_idx2 = BRBE_BANK0_IDX_MAX;
> + loop2_idx1 = BRBE_BANK1_IDX_MIN;
> + loop2_idx2 = brbe_attr->brbe_nr - 1;
> + }
> +
> + select_brbe_bank(BRBE_BANK_IDX_0);
> + for (idx = 0, count = loop1_idx1; count <= loop1_idx2; idx++, count++) {
> + buf[idx].brbinf = get_brbinf_reg(idx);
> + /*
> + * There are no valid entries anymore on the buffer.
> + * Abort the branch record processing to save some
> + * cycles and also reduce the capture/process load
> + * for the user space as well.
> + */
> + if (brbe_invalid(buf[idx].brbinf))
> + return idx;
> +
> + buf[idx].brbsrc = get_brbsrc_reg(idx);
> + buf[idx].brbtgt = get_brbtgt_reg(idx);
> + }
> +
> + select_brbe_bank(BRBE_BANK_IDX_1);
> + for (count = loop2_idx1; count <= loop2_idx2; idx++, count++) {
> + buf[idx].brbinf = get_brbinf_reg(idx);
> + /*
> + * There are no valid entries anymore on the buffer.
> + * Abort the branch record processing to save some
> + * cycles and also reduce the capture/process load
> + * for the user space as well.
> + */
> + if (brbe_invalid(buf[idx].brbinf))
> + return idx;
> +
> + buf[idx].brbsrc = get_brbsrc_reg(idx);
> + buf[idx].brbtgt = get_brbtgt_reg(idx);
> + }
> + return idx;
> +}
As with __armv8pmu_branch_read(), the loop conditions are a bit hard to follow,
and I believe that can be rewritten along the lines of the suggestion there.
Looking at this, we now have a couple of places that will try to read the
registers for an individual record, so it probably makes sense to facotr that
into a helper, e.g.
| static bool __read_brbe_regset(struct brbe_regset *entry, int idx)
| {
| u64 brbinf = get_brbinf_reg(idx);
|
| if (brbe_invalid(brbinf))
| return false;
|
| entry->brbinf = brbinf;
| entry->brbsrc = get_brbsrc_reg(idx);
| entry->brbtgt = get_brbtgt_reg(idx);
|
| return true;
| }
... which can be used here, e.g.
| /*
| * Capture all records before the first invalid record, and return the number
| * of records captured.
| */
| static int capture_brbe_regset(struct brbe_hw_attr *brbe_attr, struct brbe_regset *buf)
| {
|
| int nr_entries = brbe_attr->brbe_nr;
| int idx = 0;
|
| select_brbe_bank(BRBE_BANK_IDX_0);
| while (idx < nr_entries && IDX < BRBE_BANK0_IDX_MAX) {
| if (__read_brbe_regset(&buf[idx], idx))
| return idx;
| }
|
| select_brbe_bank(BRBE_BANK_IDX_1);
| while (idx < nr_entries && IDX < BRBE_BANK1_IDX_MAX) {
| if (__read_brbe_regset(&buf[idx], idx))
| return idx;
| }
|
| return idx;
| }
... and could be used to implement capture_branch_entry() in the patch before
this.
> +static inline void copy_brbe_regset(struct brbe_regset *src, int src_idx,
> + struct brbe_regset *dst, int dst_idx)
> +{
> + dst[dst_idx].brbinf = src[src_idx].brbinf;
> + dst[dst_idx].brbsrc = src[src_idx].brbsrc;
> + dst[dst_idx].brbtgt = src[src_idx].brbtgt;
> +}
C can do struct assignment, so this is the same as:
| static inline void copy_brbe_regset(struct brbe_regset *src, int src_idx,
| struct brbe_regset *dst, int dst_idx)
| {
| dst[dst_idx] = src[src_idx];
| }
... and given that, it would be simpler and clearer to have that directly in
the caller, so I don't think we need this helper function.
> +/*
> + * This function concatenates branch records from stored and live buffer
> + * up to maximum nr_max records and the stored buffer holds the resultant
> + * buffer. The concatenated buffer contains all the branch records from
> + * the live buffer but might contain some from stored buffer considering
> + * the maximum combined length does not exceed 'nr_max'.
> + *
> + * Stored records Live records
> + * ------------------------------------------------^
> + * | S0 | L0 | Newest |
> + * --------------------------------- |
> + * | S1 | L1 | |
> + * --------------------------------- |
> + * | S2 | L2 | |
> + * --------------------------------- |
> + * | S3 | L3 | |
> + * --------------------------------- |
> + * | S4 | L4 | nr_max
> + * --------------------------------- |
> + * | | L5 | |
> + * --------------------------------- |
> + * | | L6 | |
> + * --------------------------------- |
> + * | | L7 | |
> + * --------------------------------- |
> + * | | | |
> + * --------------------------------- |
> + * | | | Oldest |
> + * ------------------------------------------------V
> + *
> + *
> + * S0 is the newest in the stored records, where as L7 is the oldest in
> + * the live reocords. Unless the live buffer is detetcted as being full
> + * thus potentially dropping off some older records, L7 and S0 records
> + * are contiguous in time for a user task context. The stitched buffer
> + * here represents maximum possible branch records, contiguous in time.
> + *
> + * Stored records Live records
> + * ------------------------------------------------^
> + * | L0 | L0 | Newest |
> + * --------------------------------- |
> + * | L0 | L1 | |
> + * --------------------------------- |
> + * | L2 | L2 | |
> + * --------------------------------- |
> + * | L3 | L3 | |
> + * --------------------------------- |
> + * | L4 | L4 | nr_max
> + * --------------------------------- |
> + * | L5 | L5 | |
> + * --------------------------------- |
> + * | L6 | L6 | |
> + * --------------------------------- |
> + * | L7 | L7 | |
> + * --------------------------------- |
> + * | S0 | | |
> + * --------------------------------- |
> + * | S1 | | Oldest |
> + * ------------------------------------------------V
> + * | S2 | <----|
> + * ----------------- |
> + * | S3 | <----| Dropped off after nr_max
> + * ----------------- |
> + * | S4 | <----|
> + * -----------------
> + */
> +static int stitch_stored_live_entries(struct brbe_regset *stored,
> + struct brbe_regset *live,
> + int nr_stored, int nr_live,
> + int nr_max)
> +{
> + int nr_total, nr_excess, nr_last, i;
> +
> + nr_total = nr_stored + nr_live;
> + nr_excess = nr_total - nr_max;
> +
> + /* Stored branch records in stitched buffer */
> + if (nr_live == nr_max)
> + nr_stored = 0;
> + else if (nr_excess > 0)
> + nr_stored -= nr_excess;
> +
> + /* Stitched buffer branch records length */
> + if (nr_total > nr_max)
> + nr_last = nr_max;
> + else
> + nr_last = nr_total;
> +
> + /* Move stored branch records */
> + for (i = 0; i < nr_stored; i++)
> + copy_brbe_regset(stored, i, stored, nr_last - nr_stored - 1 + i);
> +
> + /* Copy live branch records */
> + for (i = 0; i < nr_live; i++)
> + copy_brbe_regset(live, i, stored, i);
> +
> + return nr_last;
> +}
I think this can be written more simply as something like:
static int stitch_stored_live_entries(struct brbe_regset *stored,
struct brbe_regset *live,
int nr_stored, int nr_live,
int nr_max)
{
int nr_move = max(nr_stored, nr_max - nr_live);
/* Move the tail of the buffer to make room for the new entries */
memmove(&stored[nr_live], &stored[0], nr_move * sizeof(*stored));
/* Copy the new entries into the head of the buffer */
memcpy(stored[0], &live[0], nr_live * sizeof(*stored));
/* Return the number of entries in the stitched buffer */
return min(nr_live + nr_stored, nr_max);
}
... or if we could save this oldest-first, we could make it a circular buffer
and avoid moving older entries.
Thanks,
Mark.
Powered by blists - more mailing lists