On Sun, Mar 06, 2022 at 03:24:56PM -0800, Andrew Morton wrote:
On Sun, 6 Mar 2022 05:26:55 +0200 Jarkko Sakkinen jarkko@kernel.org wrote:
Sometimes you might want to use MAP_POPULATE to ask a device driver to initialize the device memory in some specific manner. SGX driver can use this to request more memory by issuing ENCLS[EAUG] x86 opcode for each page in the address range.
Why is this useful? Please fully describe the benefit to kernel users. Convince us that the benefit justifies the code churn, maintenance cost and larger kernel footprint.
Do we know of any other drivers which might use this?
Brutal honesty: I don't know if any other drivers would use this but neither I would not be surprised if they did. The need for this might very well be "masked" by ioctl API's. I was first proposing a ioctl for this but Dave suggested to at least try out this route.
Add f_ops->populate() with the same parameters as f_ops->mmap() and make it conditionally called inside call_mmap(). Update call sites accodingly.
spello
Thanks, I noticed that but did not want to spam with a new version just because of that :-)
-static inline int call_mmap(struct file *file, struct vm_area_struct *vma) +static inline int call_mmap(struct file *file, struct vm_area_struct *vma, bool do_populate) {
- return file->f_op->mmap(file, vma);
- int ret = file->f_op->mmap(file, vma);
- if (!ret && do_populate && file->f_op->populate)
ret = file->f_op->populate(file, vma);- return ret;
}
Should this still be inlined?
I think it might make sense at least to have call_mmap_populate() so and mmap_region_populate() instead of putting that boolean parameter to every flow (based on Greg's feedback). But only if this implementation approach is used in the first place.
As said, I chose to use RFC to pinpoint a bottleneck for us, not claiming that this would be the best possible way to work around it.
BR, Jarkko