Re: [PATCH 3/5] s390x/pci: Shrink RPCIT ranges to registered window

[Farhan Ali <alifm@linux.ibm.com>]

On 7/6/2026 2:19 AM, Christian Borntraeger wrote:
> From: Matthew Rosato<mjrosato@linux.ibm.com>
>
> Today, if a RPCIT instruction is presented from the guest whose range
> exceeds the previously-registered IOAT, QEMU will process the range
> so long as 1) the specified range at least partially overlaps with
> what was previously registered and 2) the guest has valid IOAT entries
> in its table.  If the entries are not present (invalid), then the
> RPCIT will unnecessarily spend time reporting the invalid
> region/segment entries.
>
> Optimize this path by exiting immediately if the requested range falls
> completely outside of the previously-registered range or if the
> requested range ends before it starts (which would only occur if the
> guest-specified address + length would overflow a u64).  Otherwise,
> clamp the request to only the portion of the range that overlaps with
> what was previously registered, effectively ignoring the portion
> outside of the registered range.
>
> Cc:qemu-stable@nongnu.org
> Fixes: 5d1abf2344 ("s390x/pci: enforce zPCI state checking")
> Reviewed-by: Christian Borntraeger<borntraeger@linux.ibm.com>
> Signed-off-by: Matthew Rosato<mjrosato@linux.ibm.com>
> ---
>   hw/s390x/s390-pci-inst.c | 8 +++++++-
>   1 file changed, 7 insertions(+), 1 deletion(-)

Reviewed-by: Farhan Ali<alifm@linux.ibm.com>