[Xen-ia64-devel] [PATCH] zero extend I/O reads

[Alex Williamson <alex.williamson@xxxxxx>]

Jes Sorensen debugged an issue recently on KVM that a ld2.acq was
getting sign extended in the I/O emulation path[1][2].  This was exposed
by the VGA console hanging due to some benign looking changes to the VGA
console structure several kernel revisions back.  I remember seeing this
on Xen, but I've lost the recipe to reproduce it.  I believe the
following patch adds the same logic that is being incorporated for KVM,
but I'm unable to prove we're hitting the same issue since I can no
longer reproduce it.  Please review and apply if it looks right.
Thanks,

        Alex

[1] http://marc.info/?t=121118934000001
[2] http://marc.info/?t=121127848500008

[IA64] zero pad emulated I/O instructions

Fixes issue seen on KVM with more recent upstream changes to the VGA
console structure.

Signed-off-by: Alex Williamson <alex.williamson@xxxxxx>

--

diff -r f04ce41dab84 xen/arch/ia64/vmx/mmio.c
--- a/xen/arch/ia64/vmx/mmio.c  Tue May 20 18:54:09 2008 +0900
+++ b/xen/arch/ia64/vmx/mmio.c  Wed May 21 13:02:27 2008 -0600
@@ -171,7 +171,7 @@ static void low_mmio_access(VCPU *vcpu, 
 
     vmx_send_assist_req(v);
     if (dir == IOREQ_READ)
-        *val = p->data;
+        *val = p->data & (~0UL >> (BITS_PER_LONG - (s * 8)));
 
     return;
 }
@@ -340,7 +340,7 @@ static void legacy_io_access(VCPU *vcpu,
 
     vmx_send_assist_req(v);
     if (dir == IOREQ_READ) { // read
-        *val=p->data;
+        *val = p->data & (~0UL >> (BITS_PER_LONG - (s * 8)));
     }
 #ifdef DEBUG_PCI
     if (dir == IOREQ_WRITE)




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