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

[Paolo Bonzini]

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.

> +	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.

Paolo

> +	data->handle = sev_get_handle(kvm);
> +	data->length = len;
> +	data->address = __sev_page_pa(inpages[0]) + offset;
> +	ret = sev_issue_cmd(kvm, SEV_CMD_LAUNCH_UPDATE_DATA,
> +			data, &argp->error);
> +	if (ret)
> +		goto err_3;
> +
> +	/* update remaining pages */
> +	for (i = 1; i < nr_pages; i++) {
> +
> +		len = min_t(size_t, PAGE_SIZE, ulen);
> +		ulen -= len;
> +		data->length = len;
> +		data->address = __sev_page_pa(inpages[i]);
> +		ret = sev_issue_cmd(kvm, SEV_CMD_LAUNCH_UPDATE_DATA,
> +					data, &argp->error);
> +		if (ret)
> +			goto err_3;
> +	}