diff --git a/drivers/net/ethernet/chelsio/cxgb4/cxgb4.h b/drivers/net/ethernet/chelsio/cxgb4/cxgb4.h
index 7b5425c9c0fb9..4fd215185f937 100644
--- a/drivers/net/ethernet/chelsio/cxgb4/cxgb4.h
+++ b/drivers/net/ethernet/chelsio/cxgb4/cxgb4.h
@@ -85,7 +85,8 @@ enum {
 	MEMWIN1_BASE_T5  = 0x52000,
 	MEMWIN2_APERTURE = 65536,
 	MEMWIN2_BASE     = 0x30000,
-	MEMWIN2_BASE_T5  = 0x54000,
+	MEMWIN2_APERTURE_T5 = 131072,
+	MEMWIN2_BASE_T5  = 0x60000,
 };
 
 enum dev_master {
@@ -608,6 +609,7 @@ struct l2t_data;
 struct adapter {
 	void __iomem *regs;
 	void __iomem *bar2;
+	u32 t4_bar0;
 	struct pci_dev *pdev;
 	struct device *pdev_dev;
 	unsigned int mbox;
@@ -946,6 +948,7 @@ void t4_write_indirect(struct adapter *adap, unsigned int addr_reg,
 void t4_read_indirect(struct adapter *adap, unsigned int addr_reg,
 		      unsigned int data_reg, u32 *vals, unsigned int nregs,
 		      unsigned int start_idx);
+void t4_hw_pci_read_cfg4(struct adapter *adapter, int reg, u32 *val);
 
 struct fw_filter_wr;
 
diff --git a/drivers/net/ethernet/chelsio/cxgb4/cxgb4_main.c b/drivers/net/ethernet/chelsio/cxgb4/cxgb4_main.c
index e8e77b806c7af..524a8b2894e74 100644
--- a/drivers/net/ethernet/chelsio/cxgb4/cxgb4_main.c
+++ b/drivers/net/ethernet/chelsio/cxgb4/cxgb4_main.c
@@ -4773,20 +4773,75 @@ void t4_fatal_err(struct adapter *adap)
 	dev_alert(adap->pdev_dev, "encountered fatal error, adapter stopped\n");
 }
 
+/* Return the specified PCI-E Configuration Space register from our Physical
+ * Function.  We try first via a Firmware LDST Command since we prefer to let
+ * the firmware own all of these registers, but if that fails we go for it
+ * directly ourselves.
+ */
+static u32 t4_read_pcie_cfg4(struct adapter *adap, int reg)
+{
+	struct fw_ldst_cmd ldst_cmd;
+	u32 val;
+	int ret;
+
+	/* Construct and send the Firmware LDST Command to retrieve the
+	 * specified PCI-E Configuration Space register.
+	 */
+	memset(&ldst_cmd, 0, sizeof(ldst_cmd));
+	ldst_cmd.op_to_addrspace =
+		htonl(FW_CMD_OP(FW_LDST_CMD) |
+		      FW_CMD_REQUEST |
+		      FW_CMD_READ |
+		      FW_LDST_CMD_ADDRSPACE(FW_LDST_ADDRSPC_FUNC_PCIE));
+	ldst_cmd.cycles_to_len16 = htonl(FW_LEN16(ldst_cmd));
+	ldst_cmd.u.pcie.select_naccess = FW_LDST_CMD_NACCESS(1);
+	ldst_cmd.u.pcie.ctrl_to_fn =
+		(FW_LDST_CMD_LC | FW_LDST_CMD_FN(adap->fn));
+	ldst_cmd.u.pcie.r = reg;
+	ret = t4_wr_mbox(adap, adap->mbox, &ldst_cmd, sizeof(ldst_cmd),
+			 &ldst_cmd);
+
+	/* If the LDST Command suucceeded, exctract the returned register
+	 * value.  Otherwise read it directly ourself.
+	 */
+	if (ret == 0)
+		val = ntohl(ldst_cmd.u.pcie.data[0]);
+	else
+		t4_hw_pci_read_cfg4(adap, reg, &val);
+
+	return val;
+}
+
 static void setup_memwin(struct adapter *adap)
 {
-	u32 bar0, mem_win0_base, mem_win1_base, mem_win2_base;
+	u32 mem_win0_base, mem_win1_base, mem_win2_base, mem_win2_aperture;
 
-	bar0 = pci_resource_start(adap->pdev, 0);  /* truncation intentional */
 	if (is_t4(adap->params.chip)) {
+		u32 bar0;
+
+		/* Truncation intentional: we only read the bottom 32-bits of
+		 * the 64-bit BAR0/BAR1 ...  We use the hardware backdoor
+		 * mechanism to read BAR0 instead of using
+		 * pci_resource_start() because we could be operating from
+		 * within a Virtual Machine which is trapping our accesses to
+		 * our Configuration Space and we need to set up the PCI-E
+		 * Memory Window decoders with the actual addresses which will
+		 * be coming across the PCI-E link.
+		 */
+		bar0 = t4_read_pcie_cfg4(adap, PCI_BASE_ADDRESS_0);
+		bar0 &= PCI_BASE_ADDRESS_MEM_MASK;
+		adap->t4_bar0 = bar0;
+
 		mem_win0_base = bar0 + MEMWIN0_BASE;
 		mem_win1_base = bar0 + MEMWIN1_BASE;
 		mem_win2_base = bar0 + MEMWIN2_BASE;
+		mem_win2_aperture = MEMWIN2_APERTURE;
 	} else {
 		/* For T5, only relative offset inside the PCIe BAR is passed */
 		mem_win0_base = MEMWIN0_BASE;
-		mem_win1_base = MEMWIN1_BASE_T5;
+		mem_win1_base = MEMWIN1_BASE;
 		mem_win2_base = MEMWIN2_BASE_T5;
+		mem_win2_aperture = MEMWIN2_APERTURE_T5;
 	}
 	t4_write_reg(adap, PCIE_MEM_ACCESS_REG(PCIE_MEM_ACCESS_BASE_WIN, 0),
 		     mem_win0_base | BIR(0) |
@@ -4796,16 +4851,19 @@ static void setup_memwin(struct adapter *adap)
 		     WINDOW(ilog2(MEMWIN1_APERTURE) - 10));
 	t4_write_reg(adap, PCIE_MEM_ACCESS_REG(PCIE_MEM_ACCESS_BASE_WIN, 2),
 		     mem_win2_base | BIR(0) |
-		     WINDOW(ilog2(MEMWIN2_APERTURE) - 10));
+		     WINDOW(ilog2(mem_win2_aperture) - 10));
+	t4_read_reg(adap, PCIE_MEM_ACCESS_REG(PCIE_MEM_ACCESS_BASE_WIN, 2));
 }
 
 static void setup_memwin_rdma(struct adapter *adap)
 {
 	if (adap->vres.ocq.size) {
-		unsigned int start, sz_kb;
+		u32 start;
+		unsigned int sz_kb;
 
-		start = pci_resource_start(adap->pdev, 2) +
-			OCQ_WIN_OFFSET(adap->pdev, &adap->vres);
+		start = t4_read_pcie_cfg4(adap, PCI_BASE_ADDRESS_2);
+		start &= PCI_BASE_ADDRESS_MEM_MASK;
+		start += OCQ_WIN_OFFSET(adap->pdev, &adap->vres);
 		sz_kb = roundup_pow_of_two(adap->vres.ocq.size) >> 10;
 		t4_write_reg(adap,
 			     PCIE_MEM_ACCESS_REG(PCIE_MEM_ACCESS_BASE_WIN, 3),
diff --git a/drivers/net/ethernet/chelsio/cxgb4/t4_hw.c b/drivers/net/ethernet/chelsio/cxgb4/t4_hw.c
index 4536ea9f70186..2c3d00d77ef67 100644
--- a/drivers/net/ethernet/chelsio/cxgb4/t4_hw.c
+++ b/drivers/net/ethernet/chelsio/cxgb4/t4_hw.c
@@ -143,6 +143,30 @@ void t4_write_indirect(struct adapter *adap, unsigned int addr_reg,
 	}
 }
 
+/*
+ * Read a 32-bit PCI Configuration Space register via the PCI-E backdoor
+ * mechanism.  This guarantees that we get the real value even if we're
+ * operating within a Virtual Machine and the Hypervisor is trapping our
+ * Configuration Space accesses.
+ */
+void t4_hw_pci_read_cfg4(struct adapter *adap, int reg, u32 *val)
+{
+	u32 req = ENABLE | FUNCTION(adap->fn) | reg;
+
+	if (is_t4(adap->params.chip))
+		req |= F_LOCALCFG;
+
+	t4_write_reg(adap, PCIE_CFG_SPACE_REQ, req);
+	*val = t4_read_reg(adap, PCIE_CFG_SPACE_DATA);
+
+	/* Reset ENABLE to 0 so reads of PCIE_CFG_SPACE_DATA won't cause a
+	 * Configuration Space read.  (None of the other fields matter when
+	 * ENABLE is 0 so a simple register write is easier than a
+	 * read-modify-write via t4_set_reg_field().)
+	 */
+	t4_write_reg(adap, PCIE_CFG_SPACE_REQ, 0);
+}
+
 /*
  * Get the reply to a mailbox command and store it in @rpl in big-endian order.
  */
diff --git a/drivers/net/ethernet/chelsio/cxgb4/t4_regs.h b/drivers/net/ethernet/chelsio/cxgb4/t4_regs.h
index 3360025ad9225..f6b2ee13e715f 100644
--- a/drivers/net/ethernet/chelsio/cxgb4/t4_regs.h
+++ b/drivers/net/ethernet/chelsio/cxgb4/t4_regs.h
@@ -387,6 +387,8 @@
 #define  MSTGRPPERR      0x00000001U
 
 #define PCIE_NONFAT_ERR 0x3010
+#define PCIE_CFG_SPACE_REQ 0x3060
+#define PCIE_CFG_SPACE_DATA 0x3064
 #define PCIE_MEM_ACCESS_BASE_WIN 0x3068
 #define S_PCIEOFST       10
 #define M_PCIEOFST       0x3fffffU
@@ -399,6 +401,9 @@
 #define  WINDOW_SHIFT    0
 #define  WINDOW(x)       ((x) << WINDOW_SHIFT)
 #define PCIE_MEM_ACCESS_OFFSET 0x306c
+#define ENABLE	(1U << 30)
+#define FUNCTION(x) ((x) << 12)
+#define F_LOCALCFG    (1U << 28)
 
 #define S_PFNUM    0
 #define V_PFNUM(x) ((x) << S_PFNUM)