[xen staging-4.20] x86/emul: dump unhandled memory accesses for PVH dom0

[patchbot@xxxxxxx]

commit 48f013199a768c6204125028f09255d20c8e99fa
Author:     Roger Pau Monné <roger.pau@xxxxxxxxxx>
AuthorDate: Thu Mar 20 12:48:32 2025 +0100
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Thu Mar 20 12:48:32 2025 +0100

    x86/emul: dump unhandled memory accesses for PVH dom0
    
    A PV dom0 can map any host memory as long as it's allowed by the IO
    capability range in d->iomem_caps.  On the other hand, a PVH dom0 has no
    way to populate MMIO region onto it's p2m, so it's limited to what Xen
    initially populates on the p2m based on the host memory map and the enabled
    device BARs.
    
    Introduce a new debug build only printk that reports attempts by dom0 to
    access addresses not populated on the p2m, and not handled by any emulator.
    This is for information purposes only, but might allow getting an idea of
    what MMIO ranges might be missing on the p2m.
    
    Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
    Acked-by: Jan Beulich <jbeulich@xxxxxxxx>
    master commit: 43d8a80a0cccfe3715bb3178b5c15fb983979651
    master date: 2025-03-05 10:26:46 +0100
---
 xen/arch/x86/hvm/emulate.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/xen/arch/x86/hvm/emulate.c b/xen/arch/x86/hvm/emulate.c
index 0d90cc4598..08b9493e6d 100644
--- a/xen/arch/x86/hvm/emulate.c
+++ b/xen/arch/x86/hvm/emulate.c
@@ -337,6 +337,9 @@ static int hvmemul_do_io(
         /* If there is no suitable backing DM, just ignore accesses */
         if ( !s )
         {
+            if ( is_mmio && is_hardware_domain(currd) )
+                gdprintk(XENLOG_DEBUG, "unhandled memory %s %#lx size %u\n",
+                         dir ? "read from" : "write to", addr, size);
             rc = hvm_process_io_intercept(&null_handler, &p);
             vio->req.state = STATE_IOREQ_NONE;
         }
--
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