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;
> +     }

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