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Date: Wed, 30 Oct 2013 21:47:19 +0100
From: Frederic Weisbecker <fweisbec@...il.com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: will.deacon@....com, mingo@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [BUG] perf: arch_perf_out_copy_user default
On Wed, Oct 30, 2013 at 09:16:22PM +0100, Peter Zijlstra wrote:
> On Wed, Oct 30, 2013 at 08:50:28PM +0100, Frederic Weisbecker wrote:
> >
> > Would it make sense to rather make copy_from_user_nmi() to use a return value
> > pattern that is closer to those of the existing copy_from_user_*() ?
>
> Yeah we can do that I suppose; copy_form_user_nmi() actually uses
> __copy_from_user_inatomic() since about a week.
Ah! Looks like we can even move copy_from_user_nmi() to asm-generic/uaccess.h then.
Its fallback implementation after this patch is the same than the x86 one anyway.
Hmm but there is the range_not_ok()...
>
> Something like so I suppose.. please check, I'm in fail mode.
>
> It looks like DEFINE_OUTPUT_COPY() functions already returned the bytes
> not copied, and all its users appear to indeed expect that.
>
> ---
> arch/x86/kernel/cpu/perf_event.c | 4 ++--
> arch/x86/kernel/cpu/perf_event_intel_ds.c | 2 +-
> arch/x86/kernel/cpu/perf_event_intel_lbr.c | 2 +-
> arch/x86/lib/usercopy.c | 2 +-
> arch/x86/oprofile/backtrace.c | 4 ++--
> kernel/events/internal.h | 35 ++++++++++++++++++++++--------
> 6 files changed, 33 insertions(+), 16 deletions(-)
>
> diff --git a/arch/x86/kernel/cpu/perf_event.c b/arch/x86/kernel/cpu/perf_event.c
> index 94bf3010bb39..0fa7dbe756e6 100644
> --- a/arch/x86/kernel/cpu/perf_event.c
> +++ b/arch/x86/kernel/cpu/perf_event.c
> @@ -1998,7 +1998,7 @@ perf_callchain_user32(struct pt_regs *regs, struct perf_callchain_entry *entry)
> frame.return_address = 0;
>
> bytes = copy_from_user_nmi(&frame, fp, sizeof(frame));
> - if (bytes != sizeof(frame))
> + if (bytes != 0)
> break;
>
> if (!valid_user_frame(fp, sizeof(frame)))
> @@ -2050,7 +2050,7 @@ perf_callchain_user(struct perf_callchain_entry *entry, struct pt_regs *regs)
> frame.return_address = 0;
>
> bytes = copy_from_user_nmi(&frame, fp, sizeof(frame));
> - if (bytes != sizeof(frame))
> + if (bytes != 0)
> break;
>
> if (!valid_user_frame(fp, sizeof(frame)))
> diff --git a/arch/x86/kernel/cpu/perf_event_intel_ds.c b/arch/x86/kernel/cpu/perf_event_intel_ds.c
> index c1760ff3c757..ae96cfa5eddd 100644
> --- a/arch/x86/kernel/cpu/perf_event_intel_ds.c
> +++ b/arch/x86/kernel/cpu/perf_event_intel_ds.c
> @@ -789,7 +789,7 @@ static int intel_pmu_pebs_fixup_ip(struct pt_regs *regs)
>
> size = ip - to; /* Must fit our buffer, see above */
> bytes = copy_from_user_nmi(buf, (void __user *)to, size);
> - if (bytes != size)
> + if (bytes != 0)
> return 0;
>
> kaddr = buf;
> diff --git a/arch/x86/kernel/cpu/perf_event_intel_lbr.c b/arch/x86/kernel/cpu/perf_event_intel_lbr.c
> index 90ee6c1d0542..d82d155aca8c 100644
> --- a/arch/x86/kernel/cpu/perf_event_intel_lbr.c
> +++ b/arch/x86/kernel/cpu/perf_event_intel_lbr.c
> @@ -491,7 +491,7 @@ static int branch_type(unsigned long from, unsigned long to, int abort)
>
> /* may fail if text not present */
> bytes = copy_from_user_nmi(buf, (void __user *)from, size);
> - if (bytes != size)
> + if (bytes != 0)
> return X86_BR_NONE;
>
> addr = buf;
> diff --git a/arch/x86/lib/usercopy.c b/arch/x86/lib/usercopy.c
> index 5465b8613944..ddf9ecb53cc3 100644
> --- a/arch/x86/lib/usercopy.c
> +++ b/arch/x86/lib/usercopy.c
> @@ -31,6 +31,6 @@ copy_from_user_nmi(void *to, const void __user *from, unsigned long n)
> ret = __copy_from_user_inatomic(to, from, n);
> pagefault_enable();
>
> - return n - ret;
> + return ret;
> }
> EXPORT_SYMBOL_GPL(copy_from_user_nmi);
> diff --git a/arch/x86/oprofile/backtrace.c b/arch/x86/oprofile/backtrace.c
> index d6aa6e8315d1..5d04be5efb64 100644
> --- a/arch/x86/oprofile/backtrace.c
> +++ b/arch/x86/oprofile/backtrace.c
> @@ -47,7 +47,7 @@ dump_user_backtrace_32(struct stack_frame_ia32 *head)
> unsigned long bytes;
>
> bytes = copy_from_user_nmi(bufhead, head, sizeof(bufhead));
> - if (bytes != sizeof(bufhead))
> + if (bytes != 0)
> return NULL;
>
> fp = (struct stack_frame_ia32 *) compat_ptr(bufhead[0].next_frame);
> @@ -93,7 +93,7 @@ static struct stack_frame *dump_user_backtrace(struct stack_frame *head)
> unsigned long bytes;
>
> bytes = copy_from_user_nmi(bufhead, head, sizeof(bufhead));
> - if (bytes != sizeof(bufhead))
> + if (bytes != 0)
> return NULL;
>
> oprofile_add_trace(bufhead[0].return_address);
> diff --git a/kernel/events/internal.h b/kernel/events/internal.h
> index ca6599723be5..569b218782ad 100644
> --- a/kernel/events/internal.h
> +++ b/kernel/events/internal.h
> @@ -82,16 +82,16 @@ static inline unsigned long perf_data_size(struct ring_buffer *rb)
> }
>
> #define DEFINE_OUTPUT_COPY(func_name, memcpy_func) \
> -static inline unsigned int \
> +static inline unsigned long \
> func_name(struct perf_output_handle *handle, \
> - const void *buf, unsigned int len) \
> + const void *buf, unsigned long len) \
> { \
> unsigned long size, written; \
> \
> do { \
> - size = min_t(unsigned long, handle->size, len); \
> - \
> + size = min(handle->size, len); \
> written = memcpy_func(handle->addr, buf, size); \
> + written = size - written; \
I assume copy_from_user_inatomic() shouldn't return negative value. I'm a bit
confused by it's long return type but I haven't found a place where it returns
anything else that the bytes copied. I only checked a very few archs though.
> \
> len -= written; \
> handle->addr += written; \
> @@ -110,20 +110,37 @@ func_name(struct perf_output_handle *handle, \
> return len; \
> }
>
> -static inline int memcpy_common(void *dst, const void *src, size_t n)
> +static inline unsigned long
> +memcpy_common(void *dst, const void *src, unsigned long n)
> {
> memcpy(dst, src, n);
> - return n;
> + return 0;
> }
>
> DEFINE_OUTPUT_COPY(__output_copy, memcpy_common)
>
> -#define MEMCPY_SKIP(dst, src, n) (n)
> +static inline unsigned long
> +memcpy_skip(void *dst, const void *src, unsigned long n)
> +{
> + return 0;
> +}
>
> -DEFINE_OUTPUT_COPY(__output_skip, MEMCPY_SKIP)
> +DEFINE_OUTPUT_COPY(__output_skip, memcpy_skip)
>
> #ifndef arch_perf_out_copy_user
> -#define arch_perf_out_copy_user __copy_from_user_inatomic
> +#define arch_perf_out_copy_user arch_perf_out_copy_user
> +
> +static inline unsigned long
> +arch_perf_out_copy_user(void *dst, const void *src, unsigned long n)
> +{
> + unsigned long ret;
> +
> + pagefault_disable();
> + ret = __copy_from_user_inatomic(dst, src, n);
> + pagefault_enable();
> +
> + return ret;
> +}
> #endif
Ok, that all looks good!
Thanks!
>
> DEFINE_OUTPUT_COPY(__output_copy_user, arch_perf_out_copy_user)
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