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From c229b16ba3eb5579a9a5d470ab16dd9ad55e57d6 Mon Sep 17 00:00:00 2001
From: Igor Druzhinin <igor.druzhinin@citrix.com>
Date: Mon, 31 Oct 2022 13:28:46 +0100
Subject: [PATCH 42/87] x86/pv-shim: correct ballooning down for compat guests
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. In order to be usable as overall result, the
function accumulates args.nr_done, i.e. it initialized the field with
the start extent. Therefore non-initial requests resulting from the
split would pass too large a number into pv_shim_offline_memory().
Address that breakage by always calling pv_shim_offline_memory()
regardless of current hypercall preemption status, with a suitably
adjusted first argument. Note that this is correct also for the native
guest case: We now simply "commit" what was completed right away, rather
than at the end of a series of preemption/re-start cycles. In fact this
improves overall preemption behavior: There's no longer a potentially
big chunk of work done non-preemptively at the end of the last
"iteration".
Fixes: b2245acc60c3 ("xen/pvshim: memory hotplug")
Signed-off-by: Igor Druzhinin <igor.druzhinin@citrix.com>
Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>
master commit: 1d7fbc535d1d37bdc2cc53ede360b0f6651f7de1
master date: 2022-10-28 15:49:33 +0200
---
xen/common/memory.c | 19 +++++++------------
1 file changed, 7 insertions(+), 12 deletions(-)
diff --git a/xen/common/memory.c b/xen/common/memory.c
index 064de4ad8d66..76f8858cc379 100644
--- a/xen/common/memory.c
+++ b/xen/common/memory.c
@@ -1420,22 +1420,17 @@ long do_memory_op(unsigned long cmd, XEN_GUEST_HANDLE_PARAM(void) arg)
rc = args.nr_done;
- if ( args.preempted )
- return hypercall_create_continuation(
- __HYPERVISOR_memory_op, "lh",
- op | (rc << MEMOP_EXTENT_SHIFT), arg);
-
#ifdef CONFIG_X86
if ( pv_shim && op == XENMEM_decrease_reservation )
- /*
- * Only call pv_shim_offline_memory when the hypercall has
- * finished. Note that nr_done is used to cope in case the
- * hypercall has failed and only part of the extents where
- * processed.
- */
- pv_shim_offline_memory(args.nr_done, args.extent_order);
+ pv_shim_offline_memory(args.nr_done - start_extent,
+ args.extent_order);
#endif
+ if ( args.preempted )
+ return hypercall_create_continuation(
+ __HYPERVISOR_memory_op, "lh",
+ op | (rc << MEMOP_EXTENT_SHIFT), arg);
+
break;
case XENMEM_exchange:
--
2.37.4
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