Re: [RFC PATCH v2 26/32] kvm: svm: Add support for SEV LAUNCH_UPDATE_DATA command

[Brijesh Singh]

On 03/16/2017 05:48 AM, Paolo Bonzini wrote:
> On 02/03/2017 16:17, Brijesh Singh wrote:
> > +static struct page **sev_pin_memory(unsigned long uaddr, unsigned long ulen,
> > +				    unsigned long *n)
> > +{
> > +	struct page **pages;
> > +	int first, last;
> > +	unsigned long npages, pinned;
> > +
> > +	/* Get number of pages */
> > +	first = (uaddr & PAGE_MASK) >> PAGE_SHIFT;
> > +	last = ((uaddr + ulen - 1) & PAGE_MASK) >> PAGE_SHIFT;
> > +	npages = (last - first + 1);
> > +
> > +	pages = kzalloc(npages * sizeof(struct page *), GFP_KERNEL);
> > +	if (!pages)
> > +		return NULL;
> > +
> > +	/* pin the user virtual address */
> > +	down_read(&current->mm->mmap_sem);
> > +	pinned = get_user_pages_fast(uaddr, npages, 1, pages);
> > +	up_read(&current->mm->mmap_sem);
>
> get_user_pages_fast, like get_user_pages_unlocked, must be called
> without mmap_sem held.

Sure.

> > +	if (pinned != npages) {
> > +		printk(KERN_ERR "SEV: failed to pin  %ld pages (got %ld)\n",
> > +				npages, pinned);
> > +		goto err;
> > +	}
> > +
> > +	*n = npages;
> > +	return pages;
> > +err:
> > +	if (pinned > 0)
> > +		release_pages(pages, pinned, 0);
> > +	kfree(pages);
> > +
> > +	return NULL;
> > +}
> >
> > +	/* the array of pages returned by get_user_pages() is a page-aligned
> > +	 * memory. Since the user buffer is probably not page-aligned, we need
> > +	 * to calculate the offset within a page for first update entry.
> > +	 */
> > +	offset = uaddr & (PAGE_SIZE - 1);
> > +	len = min_t(size_t, (PAGE_SIZE - offset), ulen);
> > +	ulen -= len;
> > +
> > +	/* update first page -
> > +	 * special care need to be taken for the first page because we might
> > +	 * be dealing with offset within the page
> > +	 */
>
> No need to special case the first page; just set "offset = 0" inside the
> loop after the first iteration.

Will do.

-Brijesh