[Xen-changelog] [xen-unstable] x86 hvm: Refuse to perform __hvm_copy() work in atomic context.

[Xen patchbot-unstable <patchbot-unstable@xxxxxxxxxxxxxxxxxxx>]

# HG changeset patch
# User Keir Fraser <keir@xxxxxxx>
# Date 1290083311 0
# Node ID 7d2fdc083c9c27142f09177e5f021e390da1550f
# Parent  92bc47c81fdcb06c0b0db2399a7d58b15a533c5d
x86 hvm: Refuse to perform __hvm_copy() work in atomic context.

Soon we will properly handle paged out memory in this function by
sleeping in hypervisor context. This will require that all callers can
sleep.

If this check is too strong, we can reduce it to only applying to
guests with paging enabled (which also currently implies only guests
using Intel EPT). However my brief testing seems to indicate it works
okay.

Signed-off-by: Keir Fraser <keir@xxxxxxx>
---
 xen/arch/x86/hvm/hvm.c |    7 +++++++
 1 files changed, 7 insertions(+)

diff -r 92bc47c81fdc -r 7d2fdc083c9c xen/arch/x86/hvm/hvm.c
--- a/xen/arch/x86/hvm/hvm.c    Thu Nov 18 12:26:27 2010 +0000
+++ b/xen/arch/x86/hvm/hvm.c    Thu Nov 18 12:28:31 2010 +0000
@@ -1905,6 +1905,13 @@ static enum hvm_copy_result __hvm_copy(
     char *p;
     int count, todo = size;
 
+    /*
+     * If the required guest memory is paged out, this function may sleep.
+     * Hence we bail immediately if called from atomic context.
+     */
+    if ( in_atomic() )
+        return HVMCOPY_unhandleable;
+
     while ( todo > 0 )
     {
         count = min_t(int, PAGE_SIZE - (addr & ~PAGE_MASK), todo);

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