Re: [PATCH v3 1/5] qdev: Introduce DEFINE_PROP_RESERVED_REGION

[Markus Armbruster <armbru@redhat.com>]

Eric Auger <eric.auger@redhat.com> writes:

> Introduce a new property defining a reserved region:
> <low address>, <high address>, <type>.
>
> This will be used to encode reserved IOVA regions.
>
> For instance, in virtio-iommu use case, reserved IOVA regions
> will be passed by the machine code to the virtio-iommu-pci
> device (an array of those). The type of the reserved region
> will match the virtio_iommu_probe_resv_mem subtype value:
> - VIRTIO_IOMMU_RESV_MEM_T_RESERVED (0)
> - VIRTIO_IOMMU_RESV_MEM_T_MSI (1)
>
> on PC/Q35 machine, this will be used to inform the
> virtio-iommu-pci device it should bypass the MSI region.
> The reserved region will be: 0xfee00000, 0xfeefffff, 1.
>
> On ARM, we can declare the ITS MSI doorbell as an MSI
> region to prevent MSIs from being mapped on guest side.
>
> Signed-off-by: Eric Auger <eric.auger@redhat.com>
>
> ---
>
> v11 -> v12:
> - rename into DEFINE_PROP_RESERVED_REGION
> - do not use g_strsplit anymore, use endptr instead
> - remove 0x references
> ---
>  include/exec/memory.h        |  6 +++
>  include/hw/qdev-properties.h |  3 ++
>  include/qemu/typedefs.h      |  1 +
>  hw/core/qdev-properties.c    | 89 ++++++++++++++++++++++++++++++++++++
>  4 files changed, 99 insertions(+)
>
> diff --git a/include/exec/memory.h b/include/exec/memory.h
> index 3e00cdbbfa..3ee8224fa7 100644
> --- a/include/exec/memory.h
> +++ b/include/exec/memory.h
> @@ -57,6 +57,12 @@ struct MemoryRegionMmio {
>      CPUWriteMemoryFunc *write[3];
>  };
>  
> +struct ReservedRegion {
> +    hwaddr low;
> +    hwaddr high;
> +    unsigned int type;
> +};
> +
>  typedef struct IOMMUTLBEntry IOMMUTLBEntry;
>  
>  /* See address_space_translate: bit 0 is read, bit 1 is write.  */
> diff --git a/include/hw/qdev-properties.h b/include/hw/qdev-properties.h
> index f161604fb6..03bf850a7e 100644
> --- a/include/hw/qdev-properties.h
> +++ b/include/hw/qdev-properties.h
> @@ -19,6 +19,7 @@ extern const PropertyInfo qdev_prop_string;
>  extern const PropertyInfo qdev_prop_chr;
>  extern const PropertyInfo qdev_prop_tpm;
>  extern const PropertyInfo qdev_prop_macaddr;
> +extern const PropertyInfo qdev_prop_reserved_region;
>  extern const PropertyInfo qdev_prop_on_off_auto;
>  extern const PropertyInfo qdev_prop_multifd_compression;
>  extern const PropertyInfo qdev_prop_losttickpolicy;
> @@ -183,6 +184,8 @@ extern const PropertyInfo qdev_prop_pcie_link_width;
>      DEFINE_PROP(_n, _s, _f, qdev_prop_drive_iothread, BlockBackend *)
>  #define DEFINE_PROP_MACADDR(_n, _s, _f)         \
>      DEFINE_PROP(_n, _s, _f, qdev_prop_macaddr, MACAddr)
> +#define DEFINE_PROP_RESERVED_REGION(_n, _s, _f)         \
> +    DEFINE_PROP(_n, _s, _f, qdev_prop_reserved_region, ReservedRegion)
>  #define DEFINE_PROP_ON_OFF_AUTO(_n, _s, _f, _d) \
>      DEFINE_PROP_SIGNED(_n, _s, _f, _d, qdev_prop_on_off_auto, OnOffAuto)
>  #define DEFINE_PROP_MULTIFD_COMPRESSION(_n, _s, _f, _d) \
> diff --git a/include/qemu/typedefs.h b/include/qemu/typedefs.h
> index ecf3cde26c..85c4f891f4 100644
> --- a/include/qemu/typedefs.h
> +++ b/include/qemu/typedefs.h
> @@ -59,6 +59,7 @@ typedef struct ISABus ISABus;
>  typedef struct ISADevice ISADevice;
>  typedef struct IsaDma IsaDma;
>  typedef struct MACAddr MACAddr;
> +typedef struct ReservedRegion ReservedRegion;
>  typedef struct MachineClass MachineClass;
>  typedef struct MachineState MachineState;
>  typedef struct MemoryListener MemoryListener;
> diff --git a/hw/core/qdev-properties.c b/hw/core/qdev-properties.c
> index cc924815da..15b84adbee 100644
> --- a/hw/core/qdev-properties.c
> +++ b/hw/core/qdev-properties.c
> @@ -14,6 +14,7 @@
>  #include "qapi/visitor.h"
>  #include "chardev/char.h"
>  #include "qemu/uuid.h"
> +#include "qemu/cutils.h"
>  
>  void qdev_prop_set_after_realize(DeviceState *dev, const char *name,
>                                    Error **errp)
> @@ -577,6 +578,94 @@ const PropertyInfo qdev_prop_macaddr = {
>      .set   = set_mac,
>  };
>  
> +/* --- Reserved Region --- */
> +
> +/*
> + * accepted syntax version:
> + *   <low address>,<high address>,<type>
> + *   where low/high addresses are uint64_t in hexadecimal
> + *   and type is an unsigned integer in decimal
> + */
> +static void get_reserved_region(Object *obj, Visitor *v, const char *name,
> +                                void *opaque, Error **errp)
> +{
> +    DeviceState *dev = DEVICE(obj);
> +    Property *prop = opaque;
> +    ReservedRegion *rr = qdev_get_prop_ptr(dev, prop);
> +    char buffer[64];
> +    char *p = buffer;
> +
> +    snprintf(buffer, sizeof(buffer), "0x%"PRIx64",0x%"PRIx64",%u",
> +             rr->low, rr->high, rr->type);

Matches existing practice in other getters.  Nevertheless, I'd suggest
something like

       n = snprintf(buffer, sizeof(buffer), ...);
       assert(n < sizeof(buffer);

> +
> +    visit_type_str(v, name, &p, errp);
> +}
> +
> +static void set_reserved_region(Object *obj, Visitor *v, const char *name,
> +                                void *opaque, Error **errp)
> +{
> +    DeviceState *dev = DEVICE(obj);
> +    Property *prop = opaque;
> +    ReservedRegion *rr = qdev_get_prop_ptr(dev, prop);
> +    Error *local_err = NULL;
> +    const char *endptr;
> +    char *str;
> +    int ret;
> +
> +    if (dev->realized) {
> +        qdev_prop_set_after_realize(dev, name, errp);
> +        return;
> +    }
> +
> +    visit_type_str(v, name, &str, &local_err);
> +    if (local_err) {
> +        error_propagate(errp, local_err);
> +        return;
> +    }
> +
> +    ret = qemu_strtou64(str, &endptr, 16, &rr->low);
> +    if (ret) {
> +        error_setg(errp, "Failed to decode reserved region low addr");
> +        error_append_hint(errp,
> +                          "should be an address in hexadecimal\n");

Comes out like this:

    qemu-system-x86_64: -device ...: Failed to decode reserved region low addr
    should be an address in hexadecimal

I'd capitalize the other way, to get

    qemu-system-x86_64: -device ...: failed to decode reserved region low addr
    Should be an address in hexadecimal

Note: output is made up; I failed at figuring out how to use the new
property.  An example in PATCH 4's commit message might help.

Since the error message fails to mention @name, the user is left
guessing unless "-device ..." contains just one reserved region
parameter.

What about something like this:

           error_setg(errp, "start address of reserved region '%s'"
                      " must be a hexadecimal integer",
                      name);

No need to mess around with error_append_hint() then.

Same for the other error messages.

> +        goto out;
> +    }
> +    if (*endptr != ',') {
> +        goto separator_error;
> +    }
> +
> +    ret = qemu_strtou64(endptr + 1, &endptr, 16, &rr->high);
> +    if (ret) {
> +        error_setg(errp, "Failed to decode reserved region high addr");
> +        error_append_hint(errp,
> +                          "should be an address in hexadecimal\n");
> +        goto out;
> +    }
> +    if (*endptr != ',') {
> +        goto separator_error;
> +    }
> +
> +    ret = qemu_strtoui(endptr + 1, &endptr, 10, &rr->type);
> +    if (ret) {
> +        error_setg(errp, "Failed to decode reserved region type");
> +        error_append_hint(errp, "should be an unsigned integer in decimal\n");
> +    }

I dimly remember discussing the wisdom of numeric type here, dig, dig,
..., aha:

    Subject: Re: [PATCH for-5.0 v11 12/20] qapi: Introduce DEFINE_PROP_INTERVAL
    Date: Fri, 13 Dec 2019 11:03:02 +0100
    Message-ID: <87y2vg4k6h.fsf@dusky.pond.sub.org>

    >> So the "label" part of "<low address>,<high address>,label" is a number?
    > yes it is.
    >> 
    >> Is a number appropriate for your use case, or would an enum be better?
    > I think a number is OK. There might be other types of reserved regions
    > in the future. Also if we want to allow somebody else to reuse that
    > property in another context, I would rather leave it open?

    I'd prioritize the user interface over possible reuse (which might never
    happen).  Mind, I'm not telling you using numbers is a bad user
    interface.  In general, enums are nicer, but I don't know enough about
    this particular case.

> +    goto out;
> +
> +separator_error:
> +    error_setg(errp, "reserved region fields must be separated with commas");

I'm not sure de-duplicating this error message is worth the extra goto.

> +out:
> +    g_free(str);
> +    return;
> +}
> +
> +const PropertyInfo qdev_prop_reserved_region = {
> +    .name  = "reserved_region",
> +    .description = "Reserved Region, example: 0xFEE00000,0xFEEFFFFF,0",
> +    .get   = get_reserved_region,
> +    .set   = set_reserved_region,
> +};
> +
>  /* --- on/off/auto --- */
>  
>  const PropertyInfo qdev_prop_on_off_auto = {

Can't find anything that's actually wrong, so

Reviewed-by: Markus Armbruster <armbru@redhat.com>