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    SubjectRe: [PATCH v4 10/21] perf arm_spe: Fixup top byte for data virtual address
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    On 27/10/2020 03:09, Leo Yan wrote:
    > To establish a valid address from the address packet payload and finally
    > the address value can be used for parsing data symbol in DSO, current
    > code uses 0xff to replace the tag in the top byte of data virtual
    > address.
    >
    > So far the code only fixups top byte for the memory layouts with 4KB
    > pages, it misses to support memory layouts with 64KB pages.
    >
    > This patch adds the conditions for checking bits [55:48] are 0xf0 or
    > 0xfd, if detects the patterns it will fill 0xff into the top byte of the
    > address, also adds comment to explain the fixing up.
    >
    > Signed-off-by: Leo Yan <leo.yan@linaro.org>
    > ---
    > .../util/arm-spe-decoder/arm-spe-decoder.c | 24 ++++++++++++++++---
    > 1 file changed, 21 insertions(+), 3 deletions(-)
    >
    > diff --git a/tools/perf/util/arm-spe-decoder/arm-spe-decoder.c b/tools/perf/util/arm-spe-decoder/arm-spe-decoder.c
    > index 776b3e6628bb..e135ac01d94a 100644
    > --- a/tools/perf/util/arm-spe-decoder/arm-spe-decoder.c
    > +++ b/tools/perf/util/arm-spe-decoder/arm-spe-decoder.c
    > @@ -24,7 +24,7 @@
    >
    > static u64 arm_spe_calc_ip(int index, u64 payload)
    > {
    > - u64 ns, el;
    > + u64 ns, el, val;
    >
    > /* Instruction virtual address or Branch target address */
    > if (index == SPE_ADDR_PKT_HDR_INDEX_INS ||
    > @@ -45,8 +45,26 @@ static u64 arm_spe_calc_ip(int index, u64 payload)
    > /* Clean tags */
    > payload = SPE_ADDR_PKT_ADDR_GET_BYTES_0_6(payload);
    >
    > - /* Fill highest byte if bits [48..55] is 0xff */
    > - if (SPE_ADDR_PKT_ADDR_GET_BYTE_6(payload) == 0xffULL)
    > + /*
    > + * Armv8 ARM (ARM DDI 0487F.c), chapter "D10.2.1 Address packet"
    > + * defines the data virtual address payload format, the top byte
    > + * (bits [63:56]) is assigned as top-byte tag; so we only can
    > + * retrieve address value from bits [55:0].
    > + *
    > + * According to Documentation/arm64/memory.rst, if detects the
    > + * specific pattern in bits [55:48] of payload which falls in
    > + * the kernel space, should fixup the top byte and this allows
    > + * perf tool to parse DSO symbol for data address correctly.
    > + *
    > + * For this reason, if detects the bits [55:48] is one of
    > + * following values, will fill 0xff into the top byte:
    > + *
    > + * - 0xff (for most kernel memory regions);
    > + * - 0xf0 (for kernel logical memory map with 64KB pages);
    > + * - 0xfd (for kasan shadow region with 64KB pages).
    > + */
    > + val = SPE_ADDR_PKT_ADDR_GET_BYTE_6(payload);
    > + if (val == 0xffULL || val == 0xf0ULL || val == 0xfdULL)

    But those values are just the beginning of the region used by the
    kernel, aren't they? So the kernel logical map goes from 0xfff000.. to
    0xfff7fff..., for instance.

    But actually I wonder why were are so selective here? Wouldn't it just
    suffice to look at bits [55:52] to be either 0 or F?

    Cheers,
    Andre

    > payload |= 0xffULL << SPE_ADDR_PKT_ADDR_BYTE7_SHIFT;
    >
    > /* Data access physical address */
    >

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