[xen master] x86/vPIC: vpic_elcr_mask() master bit 2 control

[patchbot@xxxxxxx]

commit 2e5e9ec4ff900e03fb87612d968c5aaa9c9af511
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Wed Dec 6 10:22:46 2023 +0100
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Wed Dec 6 10:22:46 2023 +0100

    x86/vPIC: vpic_elcr_mask() master bit 2 control
    
    Master bit 2 is treated specially: We force it set, but we don't expose
    the bit being set to the guest. While right now the read and write
    handling can easily use the fixed mask, the restore input checking that
    is about to be put in place wants to use the inverted mask to prove that
    no bits are unduly set. That will require master bit 2 to be set. Otoh
    the read path requires the bit to be clear (the bit can have either
    value for the use on the write path). Hence allow use sites control over
    that bit.
    
    Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
    Reviewed-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
---
 xen/arch/x86/hvm/vpic.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/xen/arch/x86/hvm/vpic.c b/xen/arch/x86/hvm/vpic.c
index 938d611361..5f822844db 100644
--- a/xen/arch/x86/hvm/vpic.c
+++ b/xen/arch/x86/hvm/vpic.c
@@ -41,7 +41,7 @@
 #define vpic_lock(v)   spin_lock(__vpic_lock(v))
 #define vpic_unlock(v) spin_unlock(__vpic_lock(v))
 #define vpic_is_locked(v) spin_is_locked(__vpic_lock(v))
-#define vpic_elcr_mask(v) ((v)->is_master ? 0xf8 : 0xde)
+#define vpic_elcr_mask(v, mb2) ((v)->is_master ? 0xf8 | ((mb2) << 2) : 0xde)
 
 /* Return the highest priority found in mask. Return 8 if none. */
 #define VPIC_PRIO_NONE 8
@@ -387,7 +387,7 @@ static int cf_check vpic_intercept_elcr_io(
         if ( dir == IOREQ_WRITE )
         {
             /* Some IRs are always edge trig. Slave IR is always level trig. */
-            data = (*val >> shift) & vpic_elcr_mask(vpic);
+            data = (*val >> shift) & vpic_elcr_mask(vpic, 1);
             if ( vpic->is_master )
                 data |= 1 << 2;
             vpic->elcr = data;
@@ -395,7 +395,7 @@ static int cf_check vpic_intercept_elcr_io(
         else
         {
             /* Reader should not see hardcoded level-triggered slave IR. */
-            data = vpic->elcr & vpic_elcr_mask(vpic);
+            data = vpic->elcr & vpic_elcr_mask(vpic, 0);
             if ( !shift )
                 *val = data;
             else
--
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