[Xen-devel] [PATCH v2 02/11] ioreq: terminate cf8 handling at hypervisor level

[Roger Pau Monne <roger.pau@xxxxxxxxxx>]

Do not forward accesses to cf8 to external emulators, decoding of PCI
accesses is handled by Xen, and emulators can request handling of
config space accesses of devices using the provided ioreq interface.

Fully terminate cf8 accesses at the hypervisor level, by improving the
existing hvm_access_cf8 helper to also handle register reads, and
always return X86EMUL_OKAY in order to terminate the emulation.

Also return an error to ioreq servers attempting to map PCI IO ports
(0xcf8-cfc), as those are handled by Xen.

Note that without this change in the absence of some external emulator
that catches accesses to cf8 read requests to the register would
misbehave, as the ioreq internal handler did not handle those.

Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
---
Changes since v1:
 - New in this version.
---
 xen/arch/x86/hvm/ioreq.c | 16 +++++++++++++---
 1 file changed, 13 insertions(+), 3 deletions(-)

diff --git a/xen/arch/x86/hvm/ioreq.c b/xen/arch/x86/hvm/ioreq.c
index 692b710b02..69652e1080 100644
--- a/xen/arch/x86/hvm/ioreq.c
+++ b/xen/arch/x86/hvm/ioreq.c
@@ -1015,6 +1015,12 @@ int hvm_map_io_range_to_ioreq_server(struct domain *d, 
ioservid_t id,
     switch ( type )
     {
     case XEN_DMOP_IO_RANGE_PORT:
+        rc = -EINVAL;
+        /* PCI config space accesses are handled internally. */
+        if ( start <= 0xcf8 + 8 && 0xcf8 <= end )
+            goto out;
+        else
+            /* fallthrough. */
     case XEN_DMOP_IO_RANGE_MEMORY:
     case XEN_DMOP_IO_RANGE_PCI:
         r = s->range[type];
@@ -1518,11 +1524,15 @@ static int hvm_access_cf8(
 {
     struct domain *d = current->domain;
 
-    if ( dir == IOREQ_WRITE && bytes == 4 )
+    if ( bytes != 4 )
+        return X86EMUL_OKAY;
+
+    if ( dir == IOREQ_WRITE )
         d->arch.hvm.pci_cf8 = *val;
+    else
+        *val = d->arch.hvm.pci_cf8;
 
-    /* We always need to fall through to the catch all emulator */
-    return X86EMUL_UNHANDLEABLE;
+    return X86EMUL_OKAY;
 }
 
 void hvm_ioreq_init(struct domain *d)
-- 
2.22.0


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