Re: [PATCH kernel v7 04/31] vfio: powerpc/spapr: Use it_page_size

[Alexey Kardashevskiy]

On 04/02/2015 01:50 PM, Alex Williamson wrote:
On Thu, 2015-04-02 at 13:30 +1100, Alexey Kardashevskiy wrote:
On 04/02/2015 08:48 AM, Alex Williamson wrote:
On Sat, 2015-03-28 at 01:54 +1100, Alexey Kardashevskiy wrote:
This makes use of the it_page_size from the iommu_table struct
as page size can differ.
This replaces missing IOMMU_PAGE_SHIFT macro in commented debug code
as recently introduced IOMMU_PAGE_XXX macros do not include
IOMMU_PAGE_SHIFT.

Signed-off-by: Alexey Kardashevskiy <a...@ozlabs.ru>
Reviewed-by: David Gibson <da...@gibson.dropbear.id.au>
---
   drivers/vfio/vfio_iommu_spapr_tce.c | 26 +++++++++++++-------------
   1 file changed, 13 insertions(+), 13 deletions(-)

diff --git a/drivers/vfio/vfio_iommu_spapr_tce.c 
b/drivers/vfio/vfio_iommu_spapr_tce.c
index f835e63..8bbee22 100644
--- a/drivers/vfio/vfio_iommu_spapr_tce.c
+++ b/drivers/vfio/vfio_iommu_spapr_tce.c
@@ -91,7 +91,7 @@ static int tce_iommu_enable(struct tce_container *container)
         * enforcing the limit based on the max that the guest can map.
         */
        down_write(&current->mm->mmap_sem);
-       npages = (tbl->it_size << IOMMU_PAGE_SHIFT_4K) >> PAGE_SHIFT;
+       npages = (tbl->it_size << tbl->it_page_shift) >> PAGE_SHIFT;
        locked = current->mm->locked_vm + npages;
        lock_limit = rlimit(RLIMIT_MEMLOCK) >> PAGE_SHIFT;
        if (locked > lock_limit && !capable(CAP_IPC_LOCK)) {
@@ -120,7 +120,7 @@ static void tce_iommu_disable(struct tce_container 
*container)

        down_write(&current->mm->mmap_sem);
        current->mm->locked_vm -= (container->tbl->it_size <<
-                       IOMMU_PAGE_SHIFT_4K) >> PAGE_SHIFT;
+                       container->tbl->it_page_shift) >> PAGE_SHIFT;
        up_write(&current->mm->mmap_sem);
   }

@@ -222,7 +222,7 @@ static long tce_iommu_build(struct tce_container *container,
                                        tce, ret);
                        break;
                }
-               tce += IOMMU_PAGE_SIZE_4K;
+               tce += IOMMU_PAGE_SIZE(tbl);


Is PAGE_SIZE ever smaller than IOMMU_PAGE_SIZE(tbl)?  IOW, can the page
we got from get_user_pages_fast() ever not completely fill the tce
entry?


Yes. IOMMU_PAGE_SIZE is 4K/64K/16M (16M is with huge pages enabled in QEMU
with -mempath), PAGE_SIZE is 4K/64K (normally 64K).

Isn't that a problem then that you're filling the tce with processor
page sizes via get_user_pages_fast(), but incrementing the tce by by
IOMMU page size?  For example, if PAGE_SIZE = 4K and IOMMU_PAGE_SIZE !=
4K have we really pinned all of the memory backed by the tce?Where do
you make sure the 4K page is really contiguous for the IOMMU page?


Aaaah. This is just not supported. Instead, after the previous patch 
("vfio: powerpc/spapr: Check that TCE page size is equal to it_page_size", 
which need fixed subject), tce_page_is_contained(page4K, 64K) will return 
false and the caller - tce_iommu_build() - will return -EPERM.


--
Alexey
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