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Re: [PATCH] xen/memory: Make resource_max_frames() to return 0 on unknown type
On 17.02.25 11:18, Jan Beulich wrote:
Hello Jan
On 16.02.2025 22:19, Oleksandr Tyshchenko wrote:
From: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>
This is actually what the caller acquire_resource() expects on any kind
of error (the comment on top of resource_max_frames() also suggests that).
Otherwise, the caller will treat -errno as a valid value and propagate incorrect
nr_frames to the VM. As a possible consequence, a VM trying to query a resource
size of an unknown type will get the success result from the hypercall and
obtain
nr_frames 4294967201.
Fixes: 9244528955de ("xen/memory: Fix acquire_resource size semantics")
Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>
Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
Thanks.
albeit preferably with an addition:
--- a/xen/common/memory.c
+++ b/xen/common/memory.c
@@ -1157,7 +1157,7 @@ static unsigned int resource_max_frames(const struct
domain *d,
return d->vmtrace_size >> PAGE_SHIFT;
default:
- return -EOPNOTSUPP;
+ return 0;
}
}
Wouldn't we better accompany this by an ASSERT_UNREACHABLE() in the default
case of _acquire_resource()?
Maybe yes, as I understand, normally we won't get to this point, as an
unknown type will always be rejected earlier in resource_max_frames().
Will add.
Jan
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