Re: [Xen-devel] [v2 04/16] xen/arm: Extend copy_to_guest to support zeroing guest VA and use it

[Stefano Stabellini]

On Tue, 12 Dec 2017, Julien Grall wrote:
> The function copy_to_guest can easily be extended to support zeroing
> guest VA. To avoid using a new bit, it is considered that a NULL buffer
> (i.e buf == NULL) means the guest memory will be zeroed.
> 
> Lastly, reimplement raw_clear_guest using copy_to_guest.
> 
> Signed-off-by: Julien Grall 

Reviewed-by: Stefano Stabellini 


> ---
> Changes in v3:
> - Use vaddr_t
> ---
>  xen/arch/arm/guestcopy.c | 41 +++--
>  1 file changed, 11 insertions(+), 30 deletions(-)
> 
> diff --git a/xen/arch/arm/guestcopy.c b/xen/arch/arm/guestcopy.c
> index 12fb03dd19..ff7d15380f 100644
> --- a/xen/arch/arm/guestcopy.c
> +++ b/xen/arch/arm/guestcopy.c
> @@ -31,7 +31,16 @@ static unsigned long copy_guest(void *buf, uint64_t addr, 
> unsigned int len,
>  p = __map_domain_page(page);
>  p += offset;
>  if ( flags & COPY_to_guest )
> -memcpy(p, buf, size);
> +{
> +/*
> + * buf will be NULL when the caller request to zero the
> + * guest memory.
> + */
> +if ( buf )
> +memcpy(p, buf, size);
> +else
> +memset(p, 0, size);
> +}
>  else
>  memcpy(buf, p, size);
>  
> @@ -67,35 +76,7 @@ unsigned long raw_copy_to_guest_flush_dcache(void *to, 
> const void *from,
>  
>  unsigned long raw_clear_guest(void *to, unsigned len)
>  {
> -/* XXX needs to handle faults */
> -unsigned offset = (vaddr_t)to & ~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) to, GV2M_WRITE);
> -if ( page == NULL )
> -return len;
> -
> -p = __map_domain_page(page);
> -p += offset;
> -memset(p, 0x00, size);
> -
> -unmap_domain_page(p - offset);
> -put_page(page);
> -len -= size;
> -to += size;
> -/*
> - * After the first iteration, guest virtual address is correctly
> - * aligned to PAGE_SIZE.
> - */
> -offset = 0;
> -}
> -
> -return 0;
> +return copy_guest(NULL, (vaddr_t)to, len, COPY_to_guest);
>  }
>  
>  unsigned long raw_copy_from_guest(void *to, const void __user *from, 
> unsigned len)
> -- 
> 2.11.0
> 

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[Xen-devel] [v2 04/16] xen/arm: Extend copy_to_guest to support zeroing guest VA and use it

[Julien Grall]

The function copy_to_guest can easily be extended to support zeroing
guest VA. To avoid using a new bit, it is considered that a NULL buffer
(i.e buf == NULL) means the guest memory will be zeroed.

Lastly, reimplement raw_clear_guest using copy_to_guest.

Signed-off-by: Julien Grall 

---
Changes in v3:
- Use vaddr_t
---
 xen/arch/arm/guestcopy.c | 41 +++--
 1 file changed, 11 insertions(+), 30 deletions(-)

diff --git a/xen/arch/arm/guestcopy.c b/xen/arch/arm/guestcopy.c
index 12fb03dd19..ff7d15380f 100644
--- a/xen/arch/arm/guestcopy.c
+++ b/xen/arch/arm/guestcopy.c
@@ -31,7 +31,16 @@ static unsigned long copy_guest(void *buf, uint64_t addr, 
unsigned int len,
 p = __map_domain_page(page);
 p += offset;
 if ( flags & COPY_to_guest )
-memcpy(p, buf, size);
+{
+/*
+ * buf will be NULL when the caller request to zero the
+ * guest memory.
+ */
+if ( buf )
+memcpy(p, buf, size);
+else
+memset(p, 0, size);
+}
 else
 memcpy(buf, p, size);
 
@@ -67,35 +76,7 @@ unsigned long raw_copy_to_guest_flush_dcache(void *to, const 
void *from,
 
 unsigned long raw_clear_guest(void *to, unsigned len)
 {
-/* XXX needs to handle faults */
-unsigned offset = (vaddr_t)to & ~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) to, GV2M_WRITE);
-if ( page == NULL )
-return len;
-
-p = __map_domain_page(page);
-p += offset;
-memset(p, 0x00, size);
-
-unmap_domain_page(p - offset);
-put_page(page);
-len -= size;
-to += size;
-/*
- * After the first iteration, guest virtual address is correctly
- * aligned to PAGE_SIZE.
- */
-offset = 0;
-}
-
-return 0;
+return copy_guest(NULL, (vaddr_t)to, len, COPY_to_guest);
 }
 
 unsigned long raw_copy_from_guest(void *to, const void __user *from, unsigned 
len)
-- 
2.11.0


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