Re: [PATCH RFC 10/19] iommu/amd: Add unmap_read_dirty() support

Suravee Suthikulpanit
2022-05-31T12:40:18Z

On 4/29/22 4:09 AM, Joao Martins wrote:
> AMD implementation of unmap_read_dirty() is pretty simple as
> mostly reuses unmap code with the extra addition of marshalling
> the dirty bit into the bitmap as it walks the to-be-unmapped
> IOPTE.
>
> Extra care is taken though, to switch over to cmpxchg as opposed
> to a non-serialized store to the PTE and testing the dirty bit
> only set until cmpxchg succeeds to set to 0.
>
> Signed-off-by: Joao Martins <joao.m.martins@oracle.com>
> ---
> drivers/iommu/amd/io_pgtable.c | 44 +++++++++++++++++++++++++++++-----
> drivers/iommu/amd/iommu.c | 22 +++++++++++++++++
> 2 files changed, 60 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/iommu/amd/io_pgtable.c b/drivers/iommu/amd/io_pgtable.c
> index 8325ef193093..1868c3b58e6d 100644
> --- a/drivers/iommu/amd/io_pgtable.c
> +++ b/drivers/iommu/amd/io_pgtable.c
> @@ -355,6 +355,16 @@ static void free_clear_pte(u64 *pte, u64 pteval, struct list_head *freelist)
> free_sub_pt(pt, mode, freelist);
> }
>
> +static bool free_pte_dirty(u64 *pte, u64 pteval)

Nitpick: Since we free and clearing the dirty bit, should we change
the function name to free_clear_pte_dirty()?

> +{
> + bool dirty = false;
> +
> + while (IOMMU_PTE_DIRTY(cmpxchg64(pte, pteval, 0)))

We should use 0ULL instead of 0.

> + dirty = true;
> +
> + return dirty;
> +}
> +

Actually, what do you think if we enhance the current free_clear_pte()
to also handle the check dirty as well?

> /*
> * Generic mapping functions. It maps a physical address into a DMA
> * address space. It allocates the page table pages if necessary.
> @@ -428,10 +438,11 @@ static int iommu_v1_map_page(struct io_pgtable_ops *ops, unsigned long iova,
> return ret;
> }
>
> -static unsigned long iommu_v1_unmap_page(struct io_pgtable_ops *ops,
> - unsigned long iova,
> - size_t size,
> - struct iommu_iotlb_gather *gather)
> +static unsigned long __iommu_v1_unmap_page(struct io_pgtable_ops *ops,
> + unsigned long iova,
> + size_t size,
> + struct iommu_iotlb_gather *gather,
> + struct iommu_dirty_bitmap *dirty)
> {
> struct amd_io_pgtable *pgtable = io_pgtable_ops_to_data(ops);
> unsigned long long unmapped;
> @@ -445,11 +456,15 @@ static unsigned long iommu_v1_unmap_page(struct io_pgtable_ops *ops,
> while (unmapped < size) {
> pte = fetch_pte(pgtable, iova, &unmap_size);
> if (pte) {
> - int i, count;
> + unsigned long i, count;
> + bool pte_dirty = false;
>
> count = PAGE_SIZE_PTE_COUNT(unmap_size);
> for (i = 0; i < count; i++)
> - pte[i] = 0ULL;
> + pte_dirty |= free_pte_dirty(&pte[i], pte[i]);
> +

Actually, what if we change the existing free_clear_pte() to free_and_clear_dirty_pte(),
and incorporate the logic for

> ...
> diff --git a/drivers/iommu/amd/iommu.c b/drivers/iommu/amd/iommu.c
> index 0a86392b2367..a8fcb6e9a684 100644
> --- a/drivers/iommu/amd/iommu.c
> +++ b/drivers/iommu/amd/iommu.c
> @@ -2144,6 +2144,27 @@ static size_t amd_iommu_unmap(struct iommu_domain *dom, unsigned long iova,
> return r;
> }
>
> +static size_t amd_iommu_unmap_read_dirty(struct iommu_domain *dom,
> + unsigned long iova, size_t page_size,
> + struct iommu_iotlb_gather *gather,
> + struct iommu_dirty_bitmap *dirty)
> +{
> + struct protection_domain *domain = to_pdomain(dom);
> + struct io_pgtable_ops *ops = &domain->iop.iop.ops;
> + size_t r;
> +
> + if ((amd_iommu_pgtable == AMD_IOMMU_V1) &&
> + (domain->iop.mode == PAGE_MODE_NONE))
> + return 0;
> +
> + r = (ops->unmap_read_dirty) ?
> + ops->unmap_read_dirty(ops, iova, page_size, gather, dirty) : 0;
> +
> + amd_iommu_iotlb_gather_add_page(dom, gather, iova, page_size);
> +
> + return r;
> +}
> +

Instead of creating a new function, what if we enhance the current amd_iommu_unmap()
to also handle read dirty part as well (e.g. __amd_iommu_unmap_read_dirty()), and
then both amd_iommu_unmap() and amd_iommu_unmap_read_dirty() can call
the __amd_iommu_unmap_read_dirty()?

Best Regards,
Suravee