Re: [PATCH v2 3/7] s390/cio: Split pfn_array_alloc_pin into pieces

Farhan Ali
2019-05-15T16:04:24Z

On 05/14/2019 07:42 PM, Eric Farman wrote:
> The pfn_array_alloc_pin routine is doing too much. Today, it does the
> alloc of the pfn_array struct and its member arrays, builds the iova
> address lists out of a contiguous piece of guest memory, and asks vfio
> to pin the resulting pages.
>
> Let's effectively revert a significant portion of commit 5c1cfb1c3948
> ("vfio: ccw: refactor and improve pfn_array_alloc_pin()") such that we
> break pfn_array_alloc_pin() into its component pieces, and have one
> routine that allocates/populates the pfn_array structs, and another
> that actually pins the memory. In the future, we will be able to
> handle scenarios where pinning memory isn't actually appropriate.
>
> Signed-off-by: Eric Farman <farman@linux.ibm.com>
> ---
> drivers/s390/cio/vfio_ccw_cp.c | 64 ++++++++++++++++++++++++----------
> 1 file changed, 46 insertions(+), 18 deletions(-)
>
> diff --git a/drivers/s390/cio/vfio_ccw_cp.c b/drivers/s390/cio/vfio_ccw_cp.c
> index 41f48b8790bc..60aa784717c5 100644
> --- a/drivers/s390/cio/vfio_ccw_cp.c
> +++ b/drivers/s390/cio/vfio_ccw_cp.c
> @@ -50,28 +50,25 @@ struct ccwchain {
> };
>
> /*
> - * pfn_array_alloc_pin() - alloc memory for PFNs, then pin user pages in memory
> + * pfn_array_alloc() - alloc memory for PFNs
> * @pa: pfn_array on which to perform the operation
> - * @mdev: the mediated device to perform pin/unpin operations
> * @iova: target guest physical address
> * @len: number of bytes that should be pinned from @iova
> *
> - * Attempt to allocate memory for PFNs, and pin user pages in memory.
> + * Attempt to allocate memory for PFNs.
> *
> * Usage of pfn_array:
> * We expect (pa_nr == 0) and (pa_iova_pfn == NULL), any field in
> * this structure will be filled in by this function.
> *
> * Returns:
> - * Number of pages pinned on success.
> - * If @pa->pa_nr is not 0, or @pa->pa_iova_pfn is not NULL initially,
> - * returns -EINVAL.
> - * If no pages were pinned, returns -errno.
> + * 0 if PFNs are allocated
> + * -EINVAL if pa->pa_nr is not initially zero, or pa->pa_iova_pfn is not NULL
> + * -ENOMEM if alloc failed
> */
> -static int pfn_array_alloc_pin(struct pfn_array *pa, struct device *mdev,
> - u64 iova, unsigned int len)
> +static int pfn_array_alloc(struct pfn_array *pa, u64 iova, unsigned int len)
> {
> - int i, ret = 0;
> + int i;
>
> if (!len)
> return 0;
> @@ -97,6 +94,22 @@ static int pfn_array_alloc_pin(struct pfn_array *pa, struct device *mdev,
> for (i = 1; i < pa->pa_nr; i++)
> pa->pa_iova_pfn[i] = pa->pa_iova_pfn[i - 1] + 1;
>
> + return 0;
> +}
> +
> +/*
> + * pfn_array_pin() - Pin user pages in memory
> + * @pa: pfn_array on which to perform the operation
> + * @mdev: the mediated device to perform pin operations
> + *
> + * Returns number of pages pinned upon success.
> + * If the pin request partially succeeds, or fails completely,
> + * all pages are left unpinned and a negative error value is returned.
> + */
> +static int pfn_array_pin(struct pfn_array *pa, struct device *mdev)
> +{
> + int ret = 0;
> +
> ret = vfio_pin_pages(mdev, pa->pa_iova_pfn, pa->pa_nr,
> IOMMU_READ | IOMMU_WRITE, pa->pa_pfn);
>
> @@ -112,8 +125,6 @@ static int pfn_array_alloc_pin(struct pfn_array *pa, struct device *mdev,
>
> err_out:
> pa->pa_nr = 0;
> - kfree(pa->pa_iova_pfn);
> - pa->pa_iova_pfn = NULL;
>
> return ret;
> }
> @@ -121,7 +132,9 @@ static int pfn_array_alloc_pin(struct pfn_array *pa, struct device *mdev,
> /* Unpin the pages before releasing the memory. */
> static void pfn_array_unpin_free(struct pfn_array *pa, struct device *mdev)
> {
> - vfio_unpin_pages(mdev, pa->pa_iova_pfn, pa->pa_nr);
> + /* Only unpin if any pages were pinned to begin with */
> + if (pa->pa_nr)
> + vfio_unpin_pages(mdev, pa->pa_iova_pfn, pa->pa_nr);
> pa->pa_nr = 0;
> kfree(pa->pa_iova_pfn);
> }
> @@ -209,10 +222,16 @@ static long copy_from_iova(struct device *mdev,
> int i, ret;
> unsigned long l, m;
>
> - ret = pfn_array_alloc_pin(&pa, mdev, iova, n);
> - if (ret <= 0)
> + ret = pfn_array_alloc(&pa, iova, n);
> + if (ret < 0)
> return ret;
>
> + ret = pfn_array_pin(&pa, mdev);
> + if (ret < 0) {
> + pfn_array_unpin_free(&pa, mdev);
> + return ret;
> + }
> +
> l = n;
> for (i = 0; i < pa.pa_nr; i++) {
> from = pa.pa_pfn[i] << PAGE_SHIFT;
> @@ -559,7 +578,11 @@ static int ccwchain_fetch_direct(struct ccwchain *chain,
> if (ret)
> goto out_init;
>
> - ret = pfn_array_alloc_pin(pat->pat_pa, cp->mdev, ccw->cda, ccw->count);
> + ret = pfn_array_alloc(pat->pat_pa, ccw->cda, ccw->count);
> + if (ret < 0)
> + goto out_unpin;
> +
> + ret = pfn_array_pin(pat->pat_pa, cp->mdev);
> if (ret < 0)
> goto out_unpin;
>
> @@ -589,6 +612,7 @@ static int ccwchain_fetch_idal(struct ccwchain *chain,
> {
> struct ccw1 *ccw;
> struct pfn_array_table *pat;
> + struct pfn_array *pa;
> unsigned long *idaws;
> u64 idaw_iova;
> unsigned int idaw_nr, idaw_len;
> @@ -627,9 +651,13 @@ static int ccwchain_fetch_idal(struct ccwchain *chain,
>
> for (i = 0; i < idaw_nr; i++) {
> idaw_iova = *(idaws + i);
> + pa = pat->pat_pa + i;
> +
> + ret = pfn_array_alloc(pa, idaw_iova, 1);
> + if (ret < 0)
> + goto out_free_idaws;
>
> - ret = pfn_array_alloc_pin(pat->pat_pa + i, cp->mdev,
> - idaw_iova, 1);
> + ret = pfn_array_pin(pa, cp->mdev);
> if (ret < 0)
> goto out_free_idaws;
> }
>
Reviewed-by: Farhan Ali <alifm@linux.ibm.com>