[xen master] x86/pv-shim: correct ballooning up for compat guests

[patchbot@xxxxxxx]

commit a0bfdd201ea12aa5679bb8944d63a4e0d3c23160
Author:     Igor Druzhinin <igor.druzhinin@xxxxxxxxxx>
AuthorDate: Fri Oct 28 15:48:50 2022 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Fri Oct 28 15:48:50 2022 +0200

    x86/pv-shim: correct ballooning up for compat guests
    
    From: Igor Druzhinin <igor.druzhinin@xxxxxxxxxx>
    
    The compat layer for multi-extent memory ops may need to split incoming
    requests. Since the guest handles in the interface structures may not be
    altered, it does so by leveraging do_memory_op()'s continuation
    handling: It hands on non-initial requests with a non-zero start extent,
    with the (native) handle suitably adjusted down. As a result
    do_memory_op() sees only the first of potentially several requests with
    start extent being zero. It's only that case when the function would
    issue a call to pv_shim_online_memory(), yet the range then covers only
    the first sub-range that results from the split.
    
    Address that breakage by making a complementary call to
    pv_shim_online_memory() in compat layer.
    
    Fixes: b2245acc60c3 ("xen/pvshim: memory hotplug")
    Signed-off-by: Igor Druzhinin <igor.druzhinin@xxxxxxxxxx>
    Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
    Acked-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
    Release-acked-by: Henry Wang <Henry.Wang@xxxxxxx>
---
 xen/common/compat/memory.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/xen/common/compat/memory.c b/xen/common/compat/memory.c
index 56c7de1dea..8ca63ceda6 100644
--- a/xen/common/compat/memory.c
+++ b/xen/common/compat/memory.c
@@ -7,6 +7,7 @@ EMIT_FILE;
 #include <xen/event.h>
 #include <xen/mem_access.h>
 #include <asm/current.h>
+#include <asm/guest.h>
 #include <compat/memory.h>
 
 #define xen_domid_t domid_t
@@ -146,7 +147,10 @@ int compat_memory_op(unsigned int cmd, 
XEN_GUEST_HANDLE_PARAM(void) compat)
                 nat.rsrv->nr_extents = end_extent;
                 ++split;
             }
-
+           /* Avoid calling pv_shim_online_memory() when in a continuation. */
+           if ( pv_shim && op != XENMEM_decrease_reservation && !start_extent )
+               pv_shim_online_memory(cmp.rsrv.nr_extents - 
nat.rsrv->nr_extents,
+                                     cmp.rsrv.extent_order);
             break;
 
         case XENMEM_exchange:
--
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