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Re: [Xen-devel] [PATCH v2 2/2] xen/x86: hap: Clean-up and harden hap_enable()

On 03/03/2020 13:25, Jan Beulich wrote:
On 04.02.2020 14:06, Julien Grall wrote:
From: Julien Grall <jgrall@xxxxxxxxxx>

Unlike shadow_enable(), hap_enable() can only be called once during
domain creation and with the mode equal to mode equal to
PG_external | PG_translate | PG_refcounts.

If it were called twice, then we might have something interesting
problem as the p2m tables would be re-allocated (and therefore all the
mappings would be lost).

Add code to sanity check the mode and that the function is only called
once. Take the opportunity to an if checking that PG_translate is set.

Signed-off-by: Julien Grall <jgrall@xxxxxxxxxx>

Acked-by: Jan Beulich <jbeulich@xxxxxxxx>
preferably with the duplicate words on the second line of the description

I will remove it on commit.

I keep the check != 0 because this is consistent with the rest of the
file. If we want to omit comparison against 0, then this should be in a
separate patches converting the file.

I disagree, but not enough to make the ack dependent upon the adjustment.

--- a/xen/arch/x86/mm/hap/hap.c
+++ b/xen/arch/x86/mm/hap/hap.c
@@ -445,6 +445,13 @@ int hap_enable(struct domain *d, u32 mode)
      unsigned int i;
      int rv = 0;
+ if ( mode != (PG_external | PG_translate | PG_refcounts) )
+        return -EINVAL;
+    /* The function can only be called once */
+    if ( d->arch.paging.mode != 0 )
+        return -EEXIST;

I think if such a comment gets added, it should be unambiguous. The
function can be called once per domain, not just once in total.

I will replace with "The function can only be called one per domain".


Julien Grall

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