[xen master] x86/vpic: force int output to low when in init mode

[patchbot@xxxxxxx]

commit 1ca901c527d21c083ceb706839db2cdac102926c
Author:     Roger Pau Monné <roger.pau@xxxxxxxxxx>
AuthorDate: Tue Apr 20 11:34:53 2021 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Tue Apr 20 11:34:53 2021 +0200

    x86/vpic: force int output to low when in init mode
    
    When the PIC is on the init sequence prevent interrupt delivery. The
    state of the registers is in the process of being set during the init
    phase, so it makes sense to prevent any int line changes during that
    process.
    
    Suggested-by: Jan Beulich <jbeulich@xxxxxxxx>
    Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
    Acked-by: Jan Beulich <jbeulich@xxxxxxxx>
---
 xen/arch/x86/hvm/vpic.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/xen/arch/x86/hvm/vpic.c b/xen/arch/x86/hvm/vpic.c
index c1c1de7fd0..9195155ff0 100644
--- a/xen/arch/x86/hvm/vpic.c
+++ b/xen/arch/x86/hvm/vpic.c
@@ -101,11 +101,14 @@ static void vpic_update_int_output(struct hvm_hw_vpic 
*vpic)
     irq = vpic_get_highest_priority_irq(vpic);
     TRACE_3D(TRC_HVM_EMUL_PIC_INT_OUTPUT, vpic->int_output, vpic->is_master,
              irq);
-    if ( vpic->int_output == (irq >= 0) )
+    if ( vpic->int_output == (!vpic->init_state && irq >= 0) )
         return;
 
-    /* INT line transition L->H or H->L. */
-    vpic->int_output = !vpic->int_output;
+    /*
+     * INT line transition L->H or H->L.
+     * Force line status to L when in init mode.
+     */
+    vpic->int_output = !vpic->init_state && !vpic->int_output;
 
     if ( vpic->int_output )
     {
--
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