Re: [PATCH v3 1/2] s390x/pci: add support for guests that request direct mapping

[Thomas Huth]

On 24/01/2025 21.21, Matthew Rosato wrote:
> When receiving a guest mpcifc(4) or mpcifc(6) instruction without the T
> bit set, treat this as a request to perform direct mapping instead of
> address translation.  In order to facilitate this, pin the entirety of
> guest memory into the host iommu.
>
> Pinning for the direct mapping case is handled via vfio and its memory
> listener.  Additionally, ram discard settings are inherited from vfio:
> coordinated discards (e.g. virtio-mem) are allowed while uncoordinated
> discards (e.g. virtio-balloon) are disabled.
>
> Subsequent guest DMA operations are all expected to be of the format
> guest_phys+sdma, allowing them to be used as lookup into the host
> iommu table.
>
> Signed-off-by: Matthew Rosato <mjrosato@linux.ibm.com>
> ---
...
> diff --git a/hw/s390x/s390-pci-inst.c b/hw/s390x/s390-pci-inst.c
> index e386d75d58..4c108fa8c4 100644
> --- a/hw/s390x/s390-pci-inst.c
> +++ b/hw/s390x/s390-pci-inst.c
> @@ -16,6 +16,7 @@
>   #include "exec/memory.h"
>   #include "qemu/error-report.h"
>   #include "system/hw_accel.h"
> +#include "hw/boards.h"
>   #include "hw/pci/pci_device.h"
>   #include "hw/s390x/s390-pci-inst.h"
>   #include "hw/s390x/s390-pci-bus.h"
> @@ -1008,17 +1009,25 @@ static int reg_ioat(CPUS390XState *env, 
> S390PCIBusDevice *pbdev, ZpciFib fib,
>       }
>   
>       /* currently we only support designation type 1 with translation */
> -    if (!(dt == ZPCI_IOTA_RTTO && t)) {
> +    if (t && !(dt == ZPCI_IOTA_RTTO)) {

While you're at it, you could change that "!(dt == ZPCI_IOTA_RTTO)" into
"dt != ZPCI_IOTA_RTTO".

>           error_report("unsupported ioat dt %d t %d", dt, t);
>           s390_program_interrupt(env, PGM_OPERAND, ra);
>           return -EINVAL;
> +    } else if (!t && !pbdev->rtr_allowed) {
> +        error_report("relaxed translation not allowed");

Not sure, but maybe better use qemu_log_mask(LOG_GUEST_ERROR, ...) instead?

> +        s390_program_interrupt(env, PGM_OPERAND, ra);
> +        return -EINVAL;
>       }

 Thomas