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Re: [PATCH v2 6/6] xen_arm: Add virtual PCIe host bridge support


From: Stefano Stabellini
Subject: Re: [PATCH v2 6/6] xen_arm: Add virtual PCIe host bridge support
Date: Wed, 22 Nov 2023 14:39:46 -0800 (PST)
User-agent: Alpine 2.22 (DEB 394 2020-01-19)

+Vikram

On Tue, 21 Nov 2023, Volodymyr Babchuk wrote:
> From: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
> 
> The bridge is needed for virtio-pci support, as QEMU can emulate the
> whole bridge with any virtio-pci devices connected to it.
> 
> This patch provides a flexible way to configure PCIe brige resources
> with xenstore. We made this for several reasons:
> 
> - We don't want to clash with vPCI devices, so we need information
>   from Xen toolstack on which PCI bus to use.
> - The guest memory layout that describes these resources is not stable
>   and may vary between guests, so we cannot rely on static resources
>   to be always the same for both ends.
> - Also the device-models which run in different domains and serve
>   virtio-pci devices for the same guest should use different host
>   bridge resources for Xen to distinguish. The rule for the guest
>   device-tree generation is one PCI host bridge per backend domain.
> 
> Signed-off-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
> Signed-off-by: Volodymyr Babchuk <volodymyr_babchuk@epam.com>

There is still a discussion ongoing on xen-devel if / how to register a
PCI Root Complex or individual BDFs. In the meantime a couple of
comments.

Typically emulated devices are configured in QEMU via QEMU command line
parameters, not xenstore. If you are running QEMU in a domU (instead of
Dom0) you can always read config parameters from xenstore from a wrapper
bash script (using xenstore-read) and then pass the right command line
options to QEMU.

If you need help in adding new QEMU command line options, Vikram (CCed)
can help.


> ---
> 
> Changes from v1:
> 
>  - Renamed virtio_pci_host to pcie_host entries in XenStore, because
>  there is nothing specific to virtio-pci: any PCI device can be
>  emulated via this newly created bridge.
> ---
>  hw/arm/xen_arm.c            | 186 ++++++++++++++++++++++++++++++++++++
>  hw/xen/xen-hvm-common.c     |   9 +-
>  include/hw/xen/xen_native.h |   8 +-
>  3 files changed, 200 insertions(+), 3 deletions(-)
> 
> diff --git a/hw/arm/xen_arm.c b/hw/arm/xen_arm.c
> index b9c3ae14b6..d506d55d0f 100644
> --- a/hw/arm/xen_arm.c
> +++ b/hw/arm/xen_arm.c
> @@ -22,6 +22,7 @@
>   */
>  
>  #include "qemu/osdep.h"
> +#include "qemu/cutils.h"
>  #include "qemu/error-report.h"
>  #include "qapi/qapi-commands-migration.h"
>  #include "qapi/visitor.h"
> @@ -34,6 +35,9 @@
>  #include "hw/xen/xen-hvm-common.h"
>  #include "sysemu/tpm.h"
>  #include "hw/xen/arch_hvm.h"
> +#include "exec/address-spaces.h"
> +#include "hw/pci-host/gpex.h"
> +#include "hw/virtio/virtio-pci.h"
>  
>  #define TYPE_XEN_ARM  MACHINE_TYPE_NAME("xenpvh")
>  OBJECT_DECLARE_SIMPLE_TYPE(XenArmState, XEN_ARM)
> @@ -58,6 +62,11 @@ struct XenArmState {
>      struct {
>          uint64_t tpm_base_addr;
>      } cfg;
> +
> +    MemMapEntry pcie_mmio;
> +    MemMapEntry pcie_ecam;
> +    MemMapEntry pcie_mmio_high;
> +    int         pcie_irq;
>  };
>  
>  static MemoryRegion ram_lo, ram_hi;
> @@ -73,6 +82,7 @@ static MemoryRegion ram_lo, ram_hi;
>  #define NR_VIRTIO_MMIO_DEVICES   \
>     (GUEST_VIRTIO_MMIO_SPI_LAST - GUEST_VIRTIO_MMIO_SPI_FIRST)
>  
> +/* TODO It should be xendevicemodel_set_pci_intx_level() for PCI interrupts. 
> */
>  static void xen_set_irq(void *opaque, int irq, int level)
>  {
>      if (xendevicemodel_set_irq_level(xen_dmod, xen_domid, irq, level)) {
> @@ -129,6 +139,176 @@ static void xen_init_ram(MachineState *machine)
>      }
>  }
>  
> +static void xen_create_pcie(XenArmState *xam)
> +{
> +    MemoryRegion *mmio_alias, *mmio_alias_high, *mmio_reg;
> +    MemoryRegion *ecam_alias, *ecam_reg;
> +    DeviceState *dev;
> +    int i;
> +
> +    dev = qdev_new(TYPE_GPEX_HOST);
> +    sysbus_realize_and_unref(SYS_BUS_DEVICE(dev), &error_fatal);
> +
> +    /* Map ECAM space */
> +    ecam_alias = g_new0(MemoryRegion, 1);
> +    ecam_reg = sysbus_mmio_get_region(SYS_BUS_DEVICE(dev), 0);
> +    memory_region_init_alias(ecam_alias, OBJECT(dev), "pcie-ecam",
> +                             ecam_reg, 0, xam->pcie_ecam.size);
> +    memory_region_add_subregion(get_system_memory(), xam->pcie_ecam.base,
> +                                ecam_alias);
> +
> +    /* Map the MMIO space */
> +    mmio_alias = g_new0(MemoryRegion, 1);
> +    mmio_reg = sysbus_mmio_get_region(SYS_BUS_DEVICE(dev), 1);
> +    memory_region_init_alias(mmio_alias, OBJECT(dev), "pcie-mmio",
> +                             mmio_reg,
> +                             xam->pcie_mmio.base,
> +                             xam->pcie_mmio.size);
> +    memory_region_add_subregion(get_system_memory(), xam->pcie_mmio.base,
> +                                mmio_alias);
> +
> +    /* Map the MMIO_HIGH space */
> +    mmio_alias_high = g_new0(MemoryRegion, 1);
> +    memory_region_init_alias(mmio_alias_high, OBJECT(dev), "pcie-mmio-high",
> +                             mmio_reg,
> +                             xam->pcie_mmio_high.base,
> +                             xam->pcie_mmio_high.size);
> +    memory_region_add_subregion(get_system_memory(), 
> xam->pcie_mmio_high.base,
> +                                mmio_alias_high);
> +
> +    /* Legacy PCI interrupts (#INTA - #INTD) */
> +    for (i = 0; i < GPEX_NUM_IRQS; i++) {
> +        qemu_irq irq = qemu_allocate_irq(xen_set_irq, NULL,
> +                                         xam->pcie_irq + i);
> +
> +        sysbus_connect_irq(SYS_BUS_DEVICE(dev), i, irq);
> +        gpex_set_irq_num(GPEX_HOST(dev), i, xam->pcie_irq + i);
> +    }
> +
> +    DPRINTF("Created PCIe host bridge\n");
> +}
> +
> +static bool xen_read_pcie_prop(XenArmState *xam, unsigned int xen_domid,
> +                               const char *prop_name, unsigned long *data)
> +{
> +    char path[128], *value = NULL;
> +    unsigned int len;
> +    bool ret = true;
> +
> +    snprintf(path, sizeof(path), "device-model/%d/pcie_host/%s",
> +             xen_domid, prop_name);
> +    value = xs_read(xam->state->xenstore, XBT_NULL, path, &len);
> +
> +    if (qemu_strtou64(value, NULL, 16, data)) {
> +        error_report("xenpv: Failed to get 'pcie_host/%s' prop",
> +                     prop_name);
> +        ret = false;
> +    }
> +
> +    free(value);
> +
> +    return ret;
> +}
> +
> +static int xen_get_pcie_params(XenArmState *xam)
> +{
> +    char path[128], *value = NULL, **entries = NULL;
> +    unsigned int len, tmp;
> +    int rc = -1;
> +
> +    snprintf(path, sizeof(path), "device-model/%d/pcie_host",
> +             xen_domid);
> +    entries = xs_directory(xam->state->xenstore, XBT_NULL, path, &len);
> +    if (entries == NULL) {
> +        error_report("xenpv: 'pcie_host' dir is not present");
> +        return -1;
> +    }
> +    free(entries);
> +    if (len != 9) {
> +        error_report("xenpv: Unexpected number of entries in 'pcie_host' 
> dir");
> +        goto out;
> +    }
> +
> +    snprintf(path, sizeof(path), "device-model/%d/pcie_host/id",
> +             xen_domid);
> +    value = xs_read(xam->state->xenstore, XBT_NULL, path, &len);
> +    if (qemu_strtoui(value, NULL, 10, &tmp)) {
> +        error_report("xenpv: Failed to get 'pcie_host/id' prop");
> +        goto out;
> +    }
> +    free(value);
> +    value = NULL;
> +    if (tmp > 0xffff) {
> +        error_report("xenpv: Wrong 'pcie_host/id' value %u", tmp);
> +        goto out;
> +    }
> +    xen_pci_segment = tmp;
> +
> +    if (!xen_read_pcie_prop(xam, xen_domid, "ecam_base",
> +                            &xam->pcie_ecam.base)) {
> +        goto out;
> +    }
> +
> +    if (!xen_read_pcie_prop(xam, xen_domid, "ecam_size",
> +                            &xam->pcie_ecam.size)) {
> +        goto out;
> +    }
> +
> +    if (!xen_read_pcie_prop(xam, xen_domid, "mem_base",
> +                            &xam->pcie_mmio.base)) {
> +        goto out;
> +    }
> +
> +    if (!xen_read_pcie_prop(xam, xen_domid, "mem_size",
> +                            &xam->pcie_mmio.base)) {
> +        goto out;
> +    }
> +
> +    if (!xen_read_pcie_prop(xam, xen_domid, "prefetch_mem_base",
> +                            &xam->pcie_mmio_high.base)) {
> +        goto out;
> +    }
> +
> +    if (!xen_read_pcie_prop(xam, xen_domid, "prefetch_mem_size",
> +                            &xam->pcie_mmio_high.size)) {
> +        goto out;
> +    }
> +
> +    snprintf(path, sizeof(path), "device-model/%d/pcie_host/irq_first",
> +             xen_domid);
> +    value = xs_read(xam->state->xenstore, XBT_NULL, path, &len);
> +    if (qemu_strtoi(value, NULL, 10, &xam->pcie_irq)) {
> +        error_report("xenpv: Failed to get 'pcie_host/irq_first' prop");
> +        goto out;
> +    }
> +    free(value);
> +    value = NULL;
> +    DPRINTF("PCIe host bridge: irq_first %u\n", xam->pcie_irq);
> +
> +    snprintf(path, sizeof(path), "device-model/%d/pcie_host/num_irqs",
> +             xen_domid);
> +    value = xs_read(xam->state->xenstore, XBT_NULL, path, &len);
> +    if (qemu_strtoui(value, NULL, 10, &tmp)) {
> +        error_report("xenpv: Failed to get 'pcie_host/num_irqs' prop");
> +        goto out;
> +    }
> +    free(value);
> +    value = NULL;
> +    if (tmp != GPEX_NUM_IRQS) {
> +        error_report("xenpv: Wrong 'pcie_host/num_irqs' value %u", tmp);
> +        goto out;
> +    }
> +    DPRINTF("PCIe host bridge: num_irqs %u\n", tmp);
> +
> +    rc = 0;
> +out:
> +    if (value) {
> +        free(value);
> +    }
> +
> +    return rc;
> +}
> +
>  void arch_handle_ioreq(XenIOState *state, ioreq_t *req)
>  {
>      hw_error("Invalid ioreq type 0x%x\n", req->type);
> @@ -189,6 +369,12 @@ static void xen_arm_init(MachineState *machine)
>      xen_register_ioreq(xam->state, machine->smp.cpus, &xen_memory_listener);
>  
>      xen_create_virtio_mmio_devices(xam);
> +    if (!xen_get_pcie_params(xam)) {
> +        xen_create_pcie(xam);
> +    } else {
> +        DPRINTF("PCIe host bridge is not available,"
> +                "only virtio-mmio can be used\n");
> +    }
>  
>  #ifdef CONFIG_TPM
>      if (xam->cfg.tpm_base_addr) {
> diff --git a/hw/xen/xen-hvm-common.c b/hw/xen/xen-hvm-common.c
> index 565dc39c8f..0f78f15057 100644
> --- a/hw/xen/xen-hvm-common.c
> +++ b/hw/xen/xen-hvm-common.c
> @@ -47,6 +47,8 @@ void xen_ram_alloc(ram_addr_t ram_addr, ram_addr_t size, 
> MemoryRegion *mr,
>      g_free(pfn_list);
>  }
>  
> +uint16_t xen_pci_segment;
> +
>  static void xen_set_memory(struct MemoryListener *listener,
>                             MemoryRegionSection *section,
>                             bool add)
> @@ -382,7 +384,12 @@ static void cpu_ioreq_config(XenIOState *state, ioreq_t 
> *req)
>      }
>  
>      QLIST_FOREACH(xendev, &state->dev_list, entry) {
> -        if (xendev->sbdf != sbdf) {
> +        /*
> +         * As we append xen_pci_segment just before forming dm_op in
> +         * xen_map_pcidev() we need to check with appended xen_pci_segment
> +         * here as well.
> +         */
> +        if ((xendev->sbdf | (xen_pci_segment << 16)) != sbdf) {
>              continue;
>          }
>  
> diff --git a/include/hw/xen/xen_native.h b/include/hw/xen/xen_native.h
> index 6f09c48823..2b1debaff4 100644
> --- a/include/hw/xen/xen_native.h
> +++ b/include/hw/xen/xen_native.h
> @@ -431,6 +431,8 @@ static inline void xen_unmap_io_section(domid_t dom,
>                                                      0, start_addr, end_addr);
>  }
>  
> +extern uint16_t xen_pci_segment;
> +
>  static inline void xen_map_pcidev(domid_t dom,
>                                    ioservid_t ioservid,
>                                    PCIDevice *pci_dev)
> @@ -441,7 +443,8 @@ static inline void xen_map_pcidev(domid_t dom,
>  
>      trace_xen_map_pcidev(ioservid, pci_dev_bus_num(pci_dev),
>                           PCI_SLOT(pci_dev->devfn), PCI_FUNC(pci_dev->devfn));
> -    xendevicemodel_map_pcidev_to_ioreq_server(xen_dmod, dom, ioservid, 0,
> +    xendevicemodel_map_pcidev_to_ioreq_server(xen_dmod, dom, ioservid,
> +                                              xen_pci_segment,
>                                                pci_dev_bus_num(pci_dev),
>                                                PCI_SLOT(pci_dev->devfn),
>                                                PCI_FUNC(pci_dev->devfn));
> @@ -457,7 +460,8 @@ static inline void xen_unmap_pcidev(domid_t dom,
>  
>      trace_xen_unmap_pcidev(ioservid, pci_dev_bus_num(pci_dev),
>                             PCI_SLOT(pci_dev->devfn), 
> PCI_FUNC(pci_dev->devfn));
> -    xendevicemodel_unmap_pcidev_from_ioreq_server(xen_dmod, dom, ioservid, 0,
> +    xendevicemodel_unmap_pcidev_from_ioreq_server(xen_dmod, dom, ioservid,
> +                                                  xen_pci_segment,
>                                                    pci_dev_bus_num(pci_dev),
>                                                    PCI_SLOT(pci_dev->devfn),
>                                                    PCI_FUNC(pci_dev->devfn));
> -- 
> 2.42.0
> 



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