[Xen-devel] [PATCH v3 01/10] 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.

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 v2:
 - Allow ioreq servers to map 0xcf8 and 0xcfc, even if those are
   handled by the hypervisor.

Changes since v1:
 - New in this version.
---
 xen/arch/x86/hvm/ioreq.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/xen/arch/x86/hvm/ioreq.c b/xen/arch/x86/hvm/ioreq.c
index d347144096..5e503ce498 100644
--- a/xen/arch/x86/hvm/ioreq.c
+++ b/xen/arch/x86/hvm/ioreq.c
@@ -1518,11 +1518,15 @@ 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)
-- 
2.23.0


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