Re: [Xen-devel] [PATCH for-next 03/16] xen/arm: Extend copy_to_guest to support copying from guest VA and use it

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Thu, 23 Nov 2017, Julien Grall wrote:
> The only differences between copy_to_guest (formerly called
> raw_copy_to_guest_helper) and raw_copy_from_guest is:
>     - The direction of the memcpy
>     - The permission use for translating the address
> 
> Extend copy_to_guest to support copying from guest VA by adding using a
> bit in the flags to tell the direction of the copy.
> 
> Lastly, reimplement raw_copy_from_guest using copy_to_guest.
> 
> Signed-off-by: Julien Grall <julien.grall@xxxxxxxxxx>
> ---
>  xen/arch/arm/guestcopy.c | 46 +++++++++++++---------------------------------
>  1 file changed, 13 insertions(+), 33 deletions(-)
> 
> diff --git a/xen/arch/arm/guestcopy.c b/xen/arch/arm/guestcopy.c
> index d1cfbe922c..1ffa717ca6 100644
> --- a/xen/arch/arm/guestcopy.c
> +++ b/xen/arch/arm/guestcopy.c
> @@ -6,6 +6,8 @@
>  #include <asm/guest_access.h>
>  
>  #define COPY_flush_dcache   (1U << 0)
> +#define COPY_from_guest     (0U << 1)
> +#define COPY_to_guest       (1U << 1)
>  
>  static unsigned long copy_guest(void *buf, paddr_t addr, unsigned int len,
>                                  unsigned int flags)
> @@ -19,13 +21,18 @@ static unsigned long copy_guest(void *buf, paddr_t addr, 
> unsigned int len,
>          unsigned size = min(len, (unsigned)PAGE_SIZE - offset);
>          struct page_info *page;
>  
> -        page = get_page_from_gva(current, addr, GV2M_WRITE);
> +        page = get_page_from_gva(current, addr,
> +                                 (flags & COPY_to_guest) ? GV2M_WRITE : 
> GV2M_READ);
>          if ( page == NULL )
>              return len;
>  
>          p = __map_domain_page(page);
>          p += offset;
> -        memcpy(p, buf, size);
> +        if ( flags & COPY_to_guest )
> +            memcpy(p, buf, size);
> +        else
> +            memcpy(buf, p, size);
> +
>          if ( flags & COPY_flush_dcache )
>              clean_dcache_va_range(p, size);
>  
> @@ -46,13 +53,14 @@ static unsigned long copy_guest(void *buf, paddr_t addr, 
> unsigned int len,
>  
>  unsigned long raw_copy_to_guest(void *to, const void *from, unsigned len)
>  {
> -    return copy_guest((void *)from, (unsigned long)to, len, 0);
> +    return copy_guest((void *)from, (unsigned long)to, len, COPY_to_guest);
>  }
>  
>  unsigned long raw_copy_to_guest_flush_dcache(void *to, const void *from,
>                                               unsigned len)
>  {
> -    return copy_guest((void *)from, (unsigned long)to, len, 
> COPY_flush_dcache);
> +    return copy_guest((void *)from, (unsigned long)to, len,
> +                      COPY_to_guest | COPY_flush_dcache);
>  }
>  
>  unsigned long raw_clear_guest(void *to, unsigned len)
> @@ -90,35 +98,7 @@ unsigned long raw_clear_guest(void *to, unsigned len)
>  
>  unsigned long raw_copy_from_guest(void *to, const void __user *from, 
> unsigned len)
>  {
> -    unsigned offset = (vaddr_t)from & ~PAGE_MASK;
> -
> -    while ( len )
> -    {
> -        void *p;
> -        unsigned size = min(len, (unsigned)(PAGE_SIZE - offset));
> -        struct page_info *page;
> -
> -        page = get_page_from_gva(current, (vaddr_t) from, GV2M_READ);
> -        if ( page == NULL )
> -            return len;
> -
> -        p = __map_domain_page(page);
> -        p += ((vaddr_t)from & (~PAGE_MASK));
> -
> -        memcpy(to, p, size);
> -
> -        unmap_domain_page(p);
> -        put_page(page);
> -        len -= size;
> -        from += size;
> -        to += size;
> -        /*
> -         * After the first iteration, guest virtual address is correctly
> -         * aligned to PAGE_SIZE.
> -         */
> -        offset = 0;
> -    }
> -    return 0;
> +    return copy_guest(to, (unsigned long)from, len, COPY_from_guest);
>  }

Same question about vaddr_t for the cast.

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