On 22/11/2023 15:42, David Woodhouse wrote:
On Wed, 2023-11-22 at 22:27 +0800, Xu Yilun wrote:
On Wed, Nov 22, 2023 at 09:12:18AM +0000, David Woodhouse wrote:
On Wed, 2023-11-22 at 16:54 +0800, Xu Yilun wrote:
@@ -259,13 +258,25 @@ static int __kvm_gpc_refresh(struct gfn_to_pfn_cache *gpc, gpa_t gpa,
ret = -EFAULT;
goto out;
}
+
+ hva_change = true;
+ } else {
+ /*
+ * No need to do any re-mapping if the only thing that has
+ * changed is the page offset. Just page align it to allow the
+ * new offset to be added in.
I don't understand how the uhva('s offset) could be changed when both gpa and
slot are not changed. Maybe I have no knowledge of xen, but in later
patch you said your uhva would never change...
It doesn't change on a normal refresh with kvm_gpc_refresh(), which is
just for revalidation after memslot changes or MMU invalidation.
But it can change if the gpc is being reinitialized with a new address
(perhaps because the guest has made another hypercall to set the
address, etc.)
That new address could happen to be in the *same* page as the previous
In this case, the lower bits of new gpa should be different to gpc->gpa,
so will hit "if (gpc->gpa != gpa ...)" branch.
I think that 'if (gpc->gpa != gpa); branch is also gratuitously
refreshing when it doesn't need to; it only needs to refresh if the
*aligned* gpas don't match.
I did look at that but decided that gfn_to_hva_memslot() was
sufficiently lightweight that it was not really worth optimising.
But it was like that already, so I won't heckle Paul any further :)
I appreciate it! :-)
Paul
