[PATCH v2 2/3] KVM: arm64: Fix rollback in hyp_trace_buffer_share_hyp()

[Vincent Donnefort]

When sharing the trace buffer with the hypervisor, if sharing a page
fails, the rollback path in hyp_trace_buffer_share_hyp() misses
unsharing the metadata page (meta_va) which was successfully shared
before entering the page sharing loop.

Additionally, if a failure occurs, the cleanup calls
hyp_trace_buffer_unshare_hyp() with an incorrect CPU index.  Since that
CPU's pages were already rolled back locally in the loop, this leads to
duplicate unsharing attempts.

Fix both issues affecting the rollback.

Fixes: 3aed038aac8d ("KVM: arm64: Add trace remote for the nVHE/pKVM hyp")
Reported-by: Sashiko <sashiko-bot at kernel.org>
Signed-off-by: Vincent Donnefort <vdonnefort at google.com>

diff --git a/arch/arm64/kvm/hyp_trace.c b/arch/arm64/kvm/hyp_trace.c
index 06805b426101..8595f9bdb3dc 100644
--- a/arch/arm64/kvm/hyp_trace.c
+++ b/arch/arm64/kvm/hyp_trace.c
@@ -212,14 +212,15 @@ static int hyp_trace_buffer_share_hyp(struct hyp_trace_buffer *trace_buffer)
 		}
 
 		if (ret) {
-			for (p--; p >= 0; p--)
+			while (--p >= 0)
 				__unshare_page(rb_desc->page_va[p]);
+			__unshare_page(rb_desc->meta_va);
 			break;
 		}
 	}
 
 	if (ret)
-		hyp_trace_buffer_unshare_hyp(trace_buffer, cpu--);
+		hyp_trace_buffer_unshare_hyp(trace_buffer, --cpu);
 
 	return ret;
 }
-- 
2.54.0.746.g67dd491aae-goog