linux-kernel - Re: [PATCH 08/16] sparc64: define untagged

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Date:   Tue, 11 Jun 2019 13:23:17 -0600
From:   Khalid Aziz <khalid.aziz@...cle.com>
To:     Christoph Hellwig <hch@....de>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Paul Burton <paul.burton@...s.com>,
        James Hogan <jhogan@...nel.org>,
        Yoshinori Sato <ysato@...rs.sourceforge.jp>,
        Rich Felker <dalias@...c.org>,
        "David S. Miller" <davem@...emloft.net>
Cc:     Nicholas Piggin <npiggin@...il.com>,
        Andrey Konovalov <andreyknvl@...gle.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        linux-mips@...r.kernel.org, linux-sh@...r.kernel.org,
        sparclinux@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        linux-mm@...ck.org, x86@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 08/16] sparc64: define untagged_addr()

On 6/11/19 8:40 AM, Christoph Hellwig wrote:
> Add a helper to untag a user pointer.  This is needed for ADI support
> in get_user_pages_fast.
> 
> Signed-off-by: Christoph Hellwig <hch@....de>
> ---
>  arch/sparc/include/asm/pgtable_64.h | 22 ++++++++++++++++++++++
>  1 file changed, 22 insertions(+)

Looks good to me.

Reviewed-by: Khalid Aziz <khalid.aziz@...cle.com>

> 
> diff --git a/arch/sparc/include/asm/pgtable_64.h b/arch/sparc/include/asm/pgtable_64.h
> index f0dcf991d27f..1904782dcd39 100644
> --- a/arch/sparc/include/asm/pgtable_64.h
> +++ b/arch/sparc/include/asm/pgtable_64.h
> @@ -1076,6 +1076,28 @@ static inline int io_remap_pfn_range(struct vm_area_struct *vma,
>  }
>  #define io_remap_pfn_range io_remap_pfn_range 
>  
> +static inline unsigned long untagged_addr(unsigned long start)
> +{
> +	if (adi_capable()) {
> +		long addr = start;
> +
> +		/* If userspace has passed a versioned address, kernel
> +		 * will not find it in the VMAs since it does not store
> +		 * the version tags in the list of VMAs. Storing version
> +		 * tags in list of VMAs is impractical since they can be
> +		 * changed any time from userspace without dropping into
> +		 * kernel. Any address search in VMAs will be done with
> +		 * non-versioned addresses. Ensure the ADI version bits
> +		 * are dropped here by sign extending the last bit before
> +		 * ADI bits. IOMMU does not implement version tags.
> +		 */
> +		return (addr << (long)adi_nbits()) >> (long)adi_nbits();
> +	}
> +
> +	return start;
> +}
> +#define untagged_addr untagged_addr
> +
>  #include <asm/tlbflush.h>
>  #include <asm-generic/pgtable.h>
>  
>