Re: [PATCH v3] KVM: s390: Fall back to short-term pinning in MAP ioctl

[Christian Borntraeger <borntraeger@linux.ibm.com>]

Am 24.07.26 um 15:39 schrieb Jaehoon Kim:
> FOLL_LONGTERM pinning fails for some memory types, such as file-backed
> guest memory. As a result, kvm_s390_adapter_map() returns -EINVAL and
> irqfd adapter registration fails even though interrupt delivery could
> still work via the existing non-atomic path.
> 
> When FOLL_LONGTERM pinning fails, verify that the page is accessible
> using a short-term pin instead. If the short-term pin succeeds, unpin
> the page and add a map entry with pinned=false to preserve MAP/UNMAP
> symmetry. The non-atomic irqfd path already performs short-term pinning
> for interrupt delivery, so this restores the previous behavior for
> memory that cannot be pinned long-term.
> 
> get_map_info() is updated to return NULL for unpinned entries so that
> the atomic irqfd fast path falls back to the non-atomic path.
> kvm_s390_adapter_unmap() and kvm_s390_unmap_all_adapters() skip dirty
> marking and unpin for unpinned entries.
> 
> Update Documentation/virt/kvm/devices/s390_flic.rst to reflect the
> new MAP/UNMAP behavior.
> 
> Fixes: c9a568838086 ("KVM: s390: Add map/unmap ioctl and clean mappings post-guest")
> Signed-off-by: Jaehoon Kim <jhkim@linux.ibm.com>
> Reviewed-by: Douglas Freimuth <freimuth@linux.ibm.com>
> Reviewed-by: Matthew Rosato <mjrosato@linux.ibm.com>

queued for kvm/master.

Doug, Jaehoon, Matt,

can you have a look at the sashiko feedback for the pre-existing issue and work on a
followup fix?