bhyve: Treat the COMMAND register for PCI passthru devices as emulated

Don't pass through writes of the command register through to the
physical device.  These registers do not need to be in sync, and in
some cases (e.g. when the guest is sizing the BAR and temporarily
disables decoding), the states need to diverge.

PR:		205549
Reviewed by:	corvink
Sponsored by:	Chelsio Communications
Differential Revision:	https://reviews.freebsd.org/D46179

usr.sbin/bhyve/pci_passthru.c

@@ -607,6 +607,7 @@ cfginit(struct pci_devinst *pi, int bus, int slot, int func)
 {
 	int error;
 	struct passthru_softc *sc;
+	uint16_t cmd;
 	uint8_t intline, intpin;
 
 	error = 1;
@@ -618,16 +619,18 @@ cfginit(struct pci_devinst *pi, int bus, int slot, int func)
 	sc->psc_sel.pc_func = func;
 
 	/*
-	 * Copy physical PCI header to virtual config space. INTLINE and INTPIN
-	 * shouldn't be aligned with their physical value and they are already set by
-	 * pci_emul_init().
+	 * Copy physical PCI header to virtual config space.  COMMAND,
+	 * INTLINE, and INTPIN shouldn't be aligned with their
+	 * physical value and they are already set by pci_emul_init().
 	 */
+	cmd = pci_get_cfgdata16(pi, PCIR_COMMAND);
 	intline = pci_get_cfgdata8(pi, PCIR_INTLINE);
 	intpin = pci_get_cfgdata8(pi, PCIR_INTPIN);
 	for (int i = 0; i <= PCIR_MAXLAT; i += 4) {
 		pci_set_cfgdata32(pi, i,
 		    pci_host_read_config(&sc->psc_sel, i, 4));
 	}
+	pci_set_cfgdata16(pi, PCIR_COMMAND, cmd);
 	pci_set_cfgdata8(pi, PCIR_INTLINE, intline);
 	pci_set_cfgdata8(pi, PCIR_INTPIN, intpin);
 
@@ -643,13 +646,6 @@ cfginit(struct pci_devinst *pi, int bus, int slot, int func)
 		goto done;
 	}
 
-	pci_host_write_config(&sc->psc_sel, PCIR_COMMAND, 2,
-	    pci_get_cfgdata16(pi, PCIR_COMMAND));
-
-	/*
-	 * We need to do this after PCIR_COMMAND got possibly updated, e.g.,
-	 * a BAR was enabled, as otherwise the PCIOCBARMMAP might fail on us.
-	 */
 	if (pci_msix_table_bar(pi) >= 0) {
 		error = init_msix_table(sc);
 		if (error != 0) {
@@ -919,7 +915,7 @@ passthru_init(struct pci_devinst *pi, nvlist_t *nvl)
 	    passthru_cfgread_emulate, passthru_cfgwrite_emulate)) != 0)
 		goto done;
 
-	/* Allow access to the physical command and status register. */
+	/* Allow access to the physical status register. */
 	if ((error = set_pcir_handler(sc, PCIR_COMMAND, 0x04, NULL, NULL)) != 0)
 		goto done;
 
@@ -1073,28 +1069,26 @@ passthru_cfgwrite_default(struct passthru_softc *sc, struct pci_devinst *pi,
 		return (0);
 	}
 
-#ifdef LEGACY_SUPPORT
 	/*
-	 * If this device does not support MSI natively then we cannot let
-	 * the guest disable legacy interrupts from the device. It is the
-	 * legacy interrupt that is triggering the virtual MSI to the guest.
+	 * The command register is emulated, but the status register
+	 * is passed through.
 	 */
-	if (sc->psc_msi.emulated && pci_msi_enabled(pi)) {
-		if (coff == PCIR_COMMAND && bytes == 2)
-			val &= ~PCIM_CMD_INTxDIS;
-	}
-#endif
-
-	pci_host_write_config(&sc->psc_sel, coff, bytes, val);
 	if (coff == PCIR_COMMAND) {
+		if (bytes <= 2)
+			return (-1);
+
+		/* Update the physical status register. */
+		pci_host_write_config(&sc->psc_sel, PCIR_STATUS, val >> 16, 2);
+
+		/* Update the virtual command register. */
 		cmd_old = pci_get_cfgdata16(pi, PCIR_COMMAND);
-		if (bytes == 1)
-			pci_set_cfgdata8(pi, PCIR_COMMAND, val);
-		else if (bytes == 2)
-			pci_set_cfgdata16(pi, PCIR_COMMAND, val);
+		pci_set_cfgdata16(pi, PCIR_COMMAND, val & 0xffff);
 		pci_emul_cmd_changed(pi, cmd_old);
+		return (0);
 	}
 
+	pci_host_write_config(&sc->psc_sel, coff, bytes, val);
+
 	return (0);
 }