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Subject: Re: [PATCH V9 1/4] perf/core: Add PERF_SAMPLE_DATA_PAGE_SIZE
To:     Peter Zijlstra <peterz@infradead.org>
Cc:     mingo@redhat.com, acme@kernel.org, linux-kernel@vger.kernel.org,
        mark.rutland@arm.com, alexander.shishkin@linux.intel.com,
        jolsa@redhat.com, eranian@google.com, ak@linux.intel.com,
        dave.hansen@intel.com, kirill.shutemov@linux.intel.com,
        mpe@ellerman.id.au, benh@kernel.crashing.org, paulus@samba.org,
        Will Deacon <will@kernel.org>,
        David Miller <davem@davemloft.net>
References: <20201001135749.2804-1-kan.liang@linux.intel.com>
 <20201001135749.2804-2-kan.liang@linux.intel.com>
 <20201009090927.GQ2611@hirez.programming.kicks-ass.net>
From:   "Liang, Kan" <kan.liang@linux.intel.com>
Message-ID: <a184fa36-a25d-cc7f-57b7-a1cf278b5465@linux.intel.com>
Date:   Fri, 9 Oct 2020 08:29:25 -0400
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On 10/9/2020 5:09 AM, Peter Zijlstra wrote:
> (we might not need the #ifdef gunk, but I've not yet dug out my cross
>   compilers this morning)
> 
> ---
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -7009,6 +7009,7 @@ static u64 perf_virt_to_phys(u64 virt)
>    */
>   static u64 __perf_get_page_size(struct mm_struct *mm, unsigned long addr)
>   {
> +	struct page *page;
>   	pgd_t *pgd;
>   	p4d_t *p4d;
>   	pud_t *pud;
> @@ -7030,15 +7031,27 @@ static u64 __perf_get_page_size(struct m
>   	if (!pud_present(*pud))
>   		return 0;
>   
> -	if (pud_leaf(*pud))
> +	if (pud_leaf(*pud)) {
> +#ifdef pud_page
> +		page = pud_page(*pud);
> +		if (PageHuge(page))
> +			return page_size(compound_head(page));

I think the page_size() returns the Kernel Page Size of a compound page.
What we want is the MMU page size.

If it's for the generic code, I think it should be a problem for X86.

Thanks,
Kan

> +#endif
>   		return 1ULL << PUD_SHIFT;
> +	}
>   
>   	pmd = pmd_offset(pud, addr);
>   	if (!pmd_present(*pmd))
>   		return 0;
>   
> -	if (pmd_leaf(*pmd))
> +	if (pmd_leaf(*pmd)) {
> +#ifdef pmd_page
> +		page = pmd_page(*pmd);
> +		if (PageHuge(page))
> +			return page_size(compound_head(page));
> +#endif
>   		return 1ULL << PMD_SHIFT;
> +	}
>   
>   	pte = pte_offset_map(pmd, addr);
>   	if (!pte_present(*pte)) {
> @@ -7046,6 +7059,10 @@ static u64 __perf_get_page_size(struct m
>   		return 0;
>   	}
>   
> +	page = pte_page(*pte);
> +	if (PageHuge(page))
> +		return page_size(compound_head(page));
> +
>   	pte_unmap(pte);
>   	return PAGE_SIZE;
>   }