[Xen-devel] [PATCH] public/hvm: Export the HVM_PARAM_CALLBACK_VIA ABI in the API

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CC: Keir Fraser <keir@xxxxxxx>
CC: Jan Beulich <JBeulich@xxxxxxxx>
CC: Tim Deegan <tim@xxxxxxx>
CC: Ian Campbell <Ian.Campbell@xxxxxxxxxx>
CC: Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>
CC: Stefano Stabellini <stefano.stabellini@xxxxxxxxxx>
CC: Shannon Zhao <zhaoshenglong@xxxxxxxxxx>

---
This ABI is utterly mad.

Despite appearing to be wrong, it is compatible with its implementation of

    enum {
        HVMIRQ_callback_none,
        HVMIRQ_callback_gsi,
        HVMIRQ_callback_pci_intx,
        HVMIRQ_callback_vector
    } callback_via_type;

Because of a sneaky:

    via_type = (uint8_t)(via >> 56) + 1;
    if ( ((via_type == HVMIRQ_callback_gsi) && (via == 0)) ||
         (via_type > HVMIRQ_callback_vector) )

I also observe:
 * GSI is actually clipped at 8 bits, rather than the documented 55
 * Attempting to use GSI 0 will actually disable callbacks
 * Xen currently ignores DOMAIN and FUNCTION from PCI_INTX.  As this has been
   broken for a very long time, it probably can't be fixed without breaking
   something else.

but lack sufficient time to fix these issues at the moment.
---
 xen/include/public/hvm/params.h | 19 +++++++++++--------
 1 file changed, 11 insertions(+), 8 deletions(-)

diff --git a/xen/include/public/hvm/params.h b/xen/include/public/hvm/params.h
index 356dfd3..fc4cdca 100644
--- a/xen/include/public/hvm/params.h
+++ b/xen/include/public/hvm/params.h
@@ -29,18 +29,21 @@
  * Parameter space for HVMOP_{set,get}_param.
  */
 
+#define HVM_PARAM_CALLBACK_IRQ 0
+
 /*
  * How should CPU0 event-channel notifications be delivered?
- * val[63:56] == 0: val[55:0] is a delivery GSI (Global System Interrupt).
- * val[63:56] == 1: val[55:0] is a delivery PCI INTx line, as follows:
- *                  Domain = val[47:32], Bus  = val[31:16],
- *                  DevFn  = val[15: 8], IntX = val[ 1: 0]
- * val[63:56] == 2: val[7:0] is a vector number, check for
- *                  XENFEAT_hvm_callback_vector to know if this delivery
- *                  method is available.
+ *
  * If val == 0 then CPU0 event-channel notifications are not delivered.
+ * If val != 0, val[63:56] encodes the type, as follows:
  */
-#define HVM_PARAM_CALLBACK_IRQ 0
+#define HVM_PARAM_CALLBACK_TYPE_GSI      0 /* val[55:0] is a delivery GSI */
+#define HVM_PARAM_CALLBACK_TYPE_PCI_INTX 1 /* val[55:0] is a delivery PCI INTx 
line:
+                                              Domain = val[47:32], Bus  = 
val[31:16],
+                                              DevFn  = val[15: 8], IntX = val[ 
1: 0] */
+#define HVM_PARAM_CALLBACK_TYPE_VECTOR   2 /* val[7:0] is a vector number, 
check for
+                                              XENFEAT_hvm_callback_vector to 
know if
+                                              this delivery method is 
available. */
 
 /*
  * These are not used by Xen. They are here for convenience of HVM-guest
-- 
2.1.4


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