On Sun, Apr 27, 2025 at 03:22:13PM +0800, Baolu Lu wrote: > On 4/26/25 13:58, Nicolin Chen wrote: > > The new vCMDQ object will be added for HW to access the guest memory for a > > HW-accelerated virtualization feature. It needs to ensure the guest memory > > pages are pinned when HW accesses them and they are contiguous in physical > > address space. > > > > This is very like the existing iommufd_access_pin_pages() that outputs the > > pinned page list for the caller to test its contiguity. > > > > Move those code from iommufd_access_pin/unpin_pages() and related function > > for a pair of iopt helpers that can be shared with the vCMDQ allocator. As > > the vCMDQ allocator will be a user-space triggered ioctl function, WARN_ON > > would not be a good fit in the new iopt_unpin_pages(), thus change them to > > use WARN_ON_ONCE instead. > > I'm uncertain, but perhaps pr_warn_ratelimited() would be a better > alternative to WARN_ON() here? WARN_ON_ONCE() generates warning messages > with kernel call traces in the kernel messages, which might lead users > to believe that something serious has happened in the kernel.
We already have similar practice, e.g. iommufd_hwpt_nested_alloc. In my review, a WARN_ON/WARN_ON_ONCE means there is a kernel bug, which shouldn't occur in the first place and isn't something that user space should concern. In case that it is hit, a WARN_ON_ONCE only spits one piece of traces that is enough for kernel folks to identify what's wrong, while pr_warn_ratelimited would likely end up with periodical warnings (more lines) that are neither related to user space nor useful for kernel. Thanks Nicolin
