Re: [Qemu-devel] [PATCH v2] s390x/pci: add common fmb

[Thomas Huth <thuth@redhat.com>]

On 2018-10-22 10:02, Yi Min Zhao wrote:
> Common function measurement block is used to report counters of
> successfully issued pcilg/stg/stb and rpcit instructions. This patch
> introduces a new struct ZpciFmb and schedules a timer callback to
> copy fmb to the guest memory at a interval time which is set to
> 4s by default. While attemping to update fmb failed, an event error
> would be generated. After pcilg/stg/stb and rpcit interception
> handlers issue successfully, increase the related counter. The guest
> could pass null address to switch off FMB and stop corresponding
> timer.
> 
> Signed-off-by: Yi Min Zhao <zyimin@linux.ibm.com>
> Reviewed-by: Pierre Morel <pmorel@linux.ibm.com>
> ---
[...]
> +static int fmb_do_update(S390PCIBusDevice *pbdev, uint8_t offset, int len)
> +{
> +    MemTxResult ret;
> +
> +    ret = address_space_write(&address_space_memory,
> +                              pbdev->fmb_addr + (uint64_t)offset,
> +                              MEMTXATTRS_UNSPECIFIED,
> +                              (uint8_t *)&pbdev->fmb + offset,
> +                              len);
> +    if (ret) {
> +        s390_pci_generate_error_event(ERR_EVENT_FMBA, pbdev->fh, pbdev->fid,
> +                                      pbdev->fmb_addr, 0);
> +        fmb_timer_free(pbdev);
> +    }
> +
> +    return ret;
> +}
> +
> +static void fmb_update(void *opaque)
> +{
> +    S390PCIBusDevice *pbdev = opaque;
> +    int64_t t = qemu_clock_get_ms(QEMU_CLOCK_VIRTUAL);
> +    uint8_t offset = offsetof(ZpciFmb, last_update);
> +
> +    /* Update U bit */
> +    pbdev->fmb.last_update |= UPDATE_U_BIT;
> +    if (fmb_do_update(pbdev, offset, sizeof(uint64_t))) {
> +        return;
> +    }
> +
> +    /* Update FMB counters */
> +    pbdev->fmb.sample++;
> +    if (fmb_do_update(pbdev, 0, sizeof(ZpciFmb))) {
> +        return;
> +    }
> +
> +    /* Clear U bit and update the time */
> +    pbdev->fmb.last_update = time2tod(qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL));
> +    pbdev->fmb.last_update &= ~UPDATE_U_BIT;
> +    if (fmb_do_update(pbdev, offset, sizeof(uint64_t))) {
> +        return;
> +    }
> +
> +    timer_mod(pbdev->fmb_timer, t + DEFAULT_MUI);
> +}

Sorry for noticing this in v1 already, but is this code endianess-safe?
I.e. can this also work with qemu-system-s390x running with TCG on a x86
host? I think you might have to use something like this here instead:

  pbdev->fmb.sample = cpu_to_be32(be32_to_cpu(pbdev->fmb.sample) + 1);

etc.

 Thomas