Re: [PATCH v5 02/10] hw/fsi: Introduce IBM's scratchpad

["Daniel P. Berrangé" <berrange@redhat.com>]

On Wed, Oct 11, 2023 at 10:13:31AM -0500, Ninad Palsule wrote:
> This is a part of patchset where scratchpad is introduced.
> 
> The scratchpad provides a set of non-functional registers. The firmware
> is free to use them, hardware does not support any special management
> support. The scratchpad registers can be read or written from LBUS
> slave.
> 
> In this model, The LBUS device is parent for the scratchpad.
> 
> Signed-off-by: Andrew Jeffery <andrew@aj.id.au>
> Signed-off-by: Cédric Le Goater <clg@kaod.org>
> Signed-off-by: Ninad Palsule <ninad@linux.ibm.com>
> ---
> v2:
> - Incorporated Joel's review comments.
> v5:
> - Incorporated review comments by Cedric.
> ---
>  include/hw/fsi/engine-scratchpad.h | 33 ++++++++++
>  hw/fsi/engine-scratchpad.c         | 99 ++++++++++++++++++++++++++++++
>  hw/fsi/Kconfig                     |  4 ++
>  hw/fsi/meson.build                 |  1 +
>  hw/fsi/trace-events                |  2 +
>  5 files changed, 139 insertions(+)
>  create mode 100644 include/hw/fsi/engine-scratchpad.h
>  create mode 100644 hw/fsi/engine-scratchpad.c
>  create mode 100644 hw/fsi/trace-events
> 
> diff --git a/include/hw/fsi/engine-scratchpad.h b/include/hw/fsi/engine-scratchpad.h
> new file mode 100644
> index 0000000000..17e9570c5c
> --- /dev/null
> +++ b/include/hw/fsi/engine-scratchpad.h
> @@ -0,0 +1,33 @@
> +/*
> + * SPDX-License-Identifier: GPL-2.0-or-later
> + * Copyright (C) 2023 IBM Corp.
> + *
> + * IBM scratchpad engne
> + */
> +#ifndef FSI_ENGINE_SCRATCHPAD_H
> +#define FSI_ENGINE_SCRATCHPAD_H
> +
> +#include "qemu/bitops.h"
> +
> +#include "hw/fsi/lbus.h"
> +
> +#define ENGINE_CONFIG_NEXT              BE_BIT(0)
> +#define ENGINE_CONFIG_VPD               BE_BIT(1)
> +#define ENGINE_CONFIG_SLOTS             BE_GENMASK(8, 15)
> +#define ENGINE_CONFIG_VERSION           BE_GENMASK(16, 19)
> +#define ENGINE_CONFIG_TYPE              BE_GENMASK(20, 27)
> +#define   ENGINE_CONFIG_TYPE_PEEK       (0x02 << 4)
> +#define   ENGINE_CONFIG_TYPE_FSI        (0x03 << 4)
> +#define   ENGINE_CONFIG_TYPE_SCRATCHPAD (0x06 << 4)
> +#define ENGINE_CONFIG_CRC              BE_GENMASK(28, 31)
> +
> +#define TYPE_SCRATCHPAD "scratchpad"
> +#define SCRATCHPAD(obj) OBJECT_CHECK(ScratchPad, (obj), TYPE_SCRATCHPAD)
> +
> +typedef struct ScratchPad {
> +        FSILBusDevice parent;
> +
> +        uint32_t reg;
> +} ScratchPad;
> +
> +#endif /* FSI_ENGINE_SCRATCHPAD_H */
> diff --git a/hw/fsi/engine-scratchpad.c b/hw/fsi/engine-scratchpad.c
> new file mode 100644
> index 0000000000..60f678eec4
> --- /dev/null
> +++ b/hw/fsi/engine-scratchpad.c
> @@ -0,0 +1,99 @@
> +/*
> + * SPDX-License-Identifier: GPL-2.0-or-later
> + * Copyright (C) 2023 IBM Corp.
> + *
> + * IBM scratchpad engine
> + */
> +
> +#include "qemu/osdep.h"
> +
> +#include "qapi/error.h"
> +#include "qemu/log.h"
> +#include "trace.h"
> +
> +#include "hw/fsi/engine-scratchpad.h"
> +
> +static uint64_t scratchpad_read(void *opaque, hwaddr addr, unsigned size)
> +{
> +    ScratchPad *s = SCRATCHPAD(opaque);
> +
> +    trace_scratchpad_read(addr, size);
> +
> +    if (addr) {
> +        qemu_log_mask(LOG_GUEST_ERROR,
> +                      "%s: Out of bounds read: 0x%"HWADDR_PRIx" for %u\n",
> +                      __func__, addr, size);

We already have a trace point in the line above. I don't think we should
be unconditionally logging errors like this, as this becomes a guest
triggerable denial of service on the host log collector for the guest.
eg it could flood the logfile connected to stderr with unlimited data
by repeatedly doing bad reads/writes.

> +        return 0;
> +    }
> +
> +    return s->reg;
> +}
> +
> +static void scratchpad_write(void *opaque, hwaddr addr, uint64_t data,
> +                                 unsigned size)
> +{
> +    ScratchPad *s = SCRATCHPAD(opaque);
> +
> +    trace_scratchpad_write(addr, size, data);
> +
> +    if (addr) {
> +        qemu_log_mask(LOG_GUEST_ERROR,
> +                      "%s: Out of bounds write: 0x%"HWADDR_PRIx" for %u\n",
> +                      __func__, addr, size);
> +        return;
> +    }
> +
> +    s->reg = data;
> +}
> +
> +static const struct MemoryRegionOps scratchpad_ops = {
> +    .read = scratchpad_read,
> +    .write = scratchpad_write,
> +    .endianness = DEVICE_BIG_ENDIAN,
> +};
> +
> +static void scratchpad_realize(DeviceState *dev, Error **errp)
> +{
> +    FSILBusDevice *ldev = FSI_LBUS_DEVICE(dev);
> +
> +    memory_region_init_io(&ldev->iomem, OBJECT(ldev), &scratchpad_ops,
> +                          ldev, TYPE_SCRATCHPAD, 0x400);
> +}
> +
> +static void scratchpad_reset(DeviceState *dev)
> +{
> +    ScratchPad *s = SCRATCHPAD(dev);
> +
> +    s->reg = 0;
> +}
> +
> +static void scratchpad_class_init(ObjectClass *klass, void *data)
> +{
> +    DeviceClass *dc = DEVICE_CLASS(klass);
> +    FSILBusDeviceClass *ldc = FSI_LBUS_DEVICE_CLASS(klass);
> +
> +    dc->realize = scratchpad_realize;
> +    dc->reset = scratchpad_reset;
> +
> +    ldc->config =
> +          ENGINE_CONFIG_NEXT            /* valid */
> +        | 0x00010000                    /* slots */
> +        | 0x00001000                    /* version */
> +        | ENGINE_CONFIG_TYPE_SCRATCHPAD /* type */
> +        | 0x00000007;                   /* crc */

More common QEMU style would be for the "|" to be on the end
of line rather than start.

End of line:

$ git grep '.*\s|\s*$' "*.c" | wc -l
5381

Start of line:

$ git grep '^\s*|\s.*' "*.c" | wc -l
581


> +}
> +
> +static const TypeInfo scratchpad_info = {
> +    .name = TYPE_SCRATCHPAD,
> +    .parent = TYPE_FSI_LBUS_DEVICE,
> +    .instance_size = sizeof(ScratchPad),
> +    .class_init = scratchpad_class_init,
> +    .class_size = sizeof(FSILBusDeviceClass),
> +};
> +
> +static void scratchpad_register_types(void)
> +{
> +    type_register_static(&scratchpad_info);
> +}
> +
> +type_init(scratchpad_register_types);
> diff --git a/hw/fsi/Kconfig b/hw/fsi/Kconfig
> index e650c660f0..f7c7fd1b28 100644
> --- a/hw/fsi/Kconfig
> +++ b/hw/fsi/Kconfig
> @@ -1,2 +1,6 @@
> +config FSI_SCRATCHPAD
> +    bool
> +    select FSI_LBUS
> +
>  config FSI_LBUS
>      bool
> diff --git a/hw/fsi/meson.build b/hw/fsi/meson.build
> index 4074d3a7d2..d45a98c223 100644
> --- a/hw/fsi/meson.build
> +++ b/hw/fsi/meson.build
> @@ -1 +1,2 @@
>  system_ss.add(when: 'CONFIG_FSI_LBUS', if_true: files('lbus.c'))
> +system_ss.add(when: 'CONFIG_FSI_SCRATCHPAD', if_true: files('engine-scratchpad.c'))
> diff --git a/hw/fsi/trace-events b/hw/fsi/trace-events
> new file mode 100644
> index 0000000000..97fd070354
> --- /dev/null
> +++ b/hw/fsi/trace-events
> @@ -0,0 +1,2 @@
> +scratchpad_read(uint64_t addr, uint32_t size) "@0x%" PRIx64 " size=%d"
> +scratchpad_write(uint64_t addr, uint32_t size, uint64_t data) "@0x%" PRIx64 " size=%d value=0x%"PRIx64
> -- 
> 2.39.2
> 

With regards,
Daniel
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