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Re: [Xen-devel] [PATCH 2/2] xen: arm: Set all bits in mfn_to_xen_entry()



Hi Chris,

On 14/08/2015 14:42, Chris (Christopher) Brand wrote:
Ensure that every bit has a specific value.

Reported-by: Julien Grall <julien.grall@xxxxxxxxxx>
Signed-off-by: Chris Brand <chris.brand@xxxxxxxxxxxx>
---
  xen/include/asm-arm/page.h | 5 +++++
  1 file changed, 5 insertions(+)

diff --git a/xen/include/asm-arm/page.h b/xen/include/asm-arm/page.h
index 01628f3e96cb..7a56b2cb463a 100644
--- a/xen/include/asm-arm/page.h
+++ b/xen/include/asm-arm/page.h
@@ -202,9 +202,14 @@ static inline lpae_t mfn_to_xen_entry(unsigned long mfn, 
unsigned attr)
              .ai = attr,
              .ns = 1,              /* Hyp mode is in the non-secure world */
              .user = 1,            /* See below */
+            .ro = 0,              /* Assume read-write */
              .af = 1,              /* No need for access tracking */
              .ng = 1,              /* Makes TLB flushes easier */
+            .sbz = 0,
+            .contig = 0,          /* Assume non-contiguous */
+            .pxn = 0,

I would add a comment to explain that this bit is reserved for PL2 stage 1 page table.

              .xn = 1,              /* No need to execute outside .text */
+            .avail = 0,

I don't think this one is necessary. avail is not used by the hardware neither Xen.

          }};;

what about *t fields (pxnt, xnt, apt,...)?

      /* Setting the User bit is strange, but the ATS1H[RW] instructions
       * don't seem to work otherwise, and since we never run on Xen


Regards,


--
Julien Grall
        

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