On Mon, Mar 18, 2019 at 07:21:09PM +0100, Jiri Olsa wrote:
> Adding perf_msr_probe function to provide interface for
> checking up on MSR register and add its related event
> attributes if it passes the check.
>
> User defines following struct for each MSR register:
>
> struct perf_msr {
> u64 msr;
> struct attribute **attrs;
> bool (*test)(int idx, void *data);
> bool no_check;
> };
>
> Where:
> msr - is the MSR address
> attrs - is attributes array to add if the check passed
> test - is test function pointer
> no_check - is bool that bypass the check and adds the
> attribute without any test
>
> The array of struct perf_msr is passed into:
>
> perf_msr_probe(struct perf_msr *msr, int cnt,
> struct attribute **attrs, void *data)
>
> Together with:
> cnt - which is the number of struct msr array elements
> attrs - which is an array placeholder for added attributes
> and needs to be big enough
> data -which is user pointer passed to the test function
>
> The perf_msr_probe will executed test code, read the MSR and
> check the value is != 0. If all these tests pass, related
> attributes are added into attrs array.
>
> Also adding MSR_ATTR macro helper to define attribute array
> from single attribute. It will be used in following patches.
Somewhere along the line you lost the explanation of _why_ we're doing
this; namely: virt sucks.
Also, recently GregKH had a chance to look at perf code and we scored
fairly high on the WTF'o'meter for what we're doing with the attribute
stuff.
He pointed me to sysfs attribute_group::is_visible functions to replace
some of our 'creative' code.
> Signed-off-by: Jiri Olsa <[email protected]>
> ---
> arch/x86/events/Makefile | 2 +-
> arch/x86/events/probe.c | 36 ++++++++++++++++++++++++++++++++++++
> arch/x86/events/probe.h | 22 ++++++++++++++++++++++
> 3 files changed, 59 insertions(+), 1 deletion(-)
> create mode 100644 arch/x86/events/probe.c
> create mode 100644 arch/x86/events/probe.h
>
> diff --git a/arch/x86/events/Makefile b/arch/x86/events/Makefile
> index b8ccdb5c9244..ec29a466444a 100644
> --- a/arch/x86/events/Makefile
> +++ b/arch/x86/events/Makefile
> @@ -1,4 +1,4 @@
> -obj-y += core.o
> +obj-y += core.o probe.o
> obj-y += amd/
> obj-$(CONFIG_X86_LOCAL_APIC) += msr.o
> obj-$(CONFIG_CPU_SUP_INTEL) += intel/
> diff --git a/arch/x86/events/probe.c b/arch/x86/events/probe.c
> new file mode 100644
> index 000000000000..0052b730c55e
> --- /dev/null
> +++ b/arch/x86/events/probe.c
> @@ -0,0 +1,36 @@
> +// SPDX-License-Identifier: GPL-2.0
> +#include <linux/export.h>
> +#include <linux/bits.h>
> +#include "probe.h"
> +
> +unsigned long
> +perf_msr_probe(struct perf_msr *msr, int cnt,
> + struct attribute **attrs, void *data)
> +{
> + unsigned long avail = 0;
> + unsigned int bit;
> + u64 val;
> +
> + if (cnt >= BITS_PER_LONG)
> + return 0;
> +
> + for (bit = 0; bit < cnt; bit++) {
> + struct attribute **a = msr[bit].attrs;
> +
> + if (!msr[bit].no_check) {
> + if (msr[bit].test && !msr[bit].test(bit, data))
> + continue;
> + if (rdmsrl_safe(msr[bit].msr, &val) || !val)
> + continue;
> + }
> +
> + while (*a)
> + *attrs++ = *a++;
> +
> + avail |= bit;
> + }
> +
> + *attrs = NULL;
> + return avail;
> +}
> +EXPORT_SYMBOL_GPL(perf_msr_probe);
> diff --git a/arch/x86/events/probe.h b/arch/x86/events/probe.h
> new file mode 100644
> index 000000000000..42dd666533c3
> --- /dev/null
> +++ b/arch/x86/events/probe.h
> @@ -0,0 +1,22 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#ifndef __ARCH_X86_EVENTS_PROBE_H__
> +#define __ARCH_X86_EVENTS_PROBE_H__
> +#include <linux/sysfs.h>
> +
> +#define MSR_ATTR(__n) \
> +static struct attribute *msr_##__n[] = { \
> + &__n.attr.attr, \
> + NULL, \
> +}
> +
> +struct perf_msr {
> + u64 msr;
> + struct attribute **attrs;
> + bool (*test)(int idx, void *data);
> + bool no_check;
> +};
> +
> +unsigned long
> +perf_msr_probe(struct perf_msr *msr, int cnt,
> + struct attribute **attrs, void *data);
> +#endif /* __ARCH_X86_EVENTS_PROBE_H__ */
> --
> 2.17.2
>
