[PATCH v4 kvmtool 05/12] pci: Limit configuration transaction size to 32 bits

[Alexandru Elisei <alexandru.elisei@arm.com>]

From PCI Local Bus Specification Revision 3.0. section 3.8 "64-Bit Bus
Extension":

"The bandwidth requirements for I/O and configuration transactions cannot
justify the added complexity, and, therefore, only memory transactions
support 64-bit data transfers".

Further down, the spec also describes the possible responses of a target
which has been requested to do a 64-bit transaction. Limit the transaction
to the lower 32 bits, to match the second accepted behaviour.

Reviewed-by: Andre Przywara <andre.przywara@arm.com>
Signed-off-by: Alexandru Elisei <alexandru.elisei@arm.com>
---
 pci.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/pci.c b/pci.c
index 81e9cec918fb..eb0bb366a291 100644
--- a/pci.c
+++ b/pci.c
@@ -119,6 +119,9 @@ static bool pci_config_data_out(struct ioport *ioport, struct kvm_cpu *vcpu, u16
 {
 	union pci_config_address pci_config_address;
 
+	if (size > 4)
+		size = 4;
+
 	pci_config_address.w = ioport__read32(&pci_config_address_bits);
 	/*
 	 * If someone accesses PCI configuration space offsets that are not
@@ -135,6 +138,9 @@ static bool pci_config_data_in(struct ioport *ioport, struct kvm_cpu *vcpu, u16
 {
 	union pci_config_address pci_config_address;
 
+	if (size > 4)
+		size = 4;
+
 	pci_config_address.w = ioport__read32(&pci_config_address_bits);
 	/*
 	 * If someone accesses PCI configuration space offsets that are not
@@ -248,6 +254,9 @@ static void pci_config_mmio_access(struct kvm_cpu *vcpu, u64 addr, u8 *data,
 	cfg_addr.w		= (u32)addr;
 	cfg_addr.enable_bit	= 1;
 
+	if (len > 4)
+		len = 4;
+
 	if (is_write)
 		pci__config_wr(kvm, cfg_addr, data, len);
 	else
-- 
2.7.4