[RFC PATCH] drm/ttm, drm/vmwgfx: Have TTM support AMD SEV encryption

Thomas Hellstrom thomas at shipmail.org
Fri May 24 09:11:54 UTC 2019


Hi, Christian,

On 5/24/19 10:37 AM, Koenig, Christian wrote:
> Am 24.05.19 um 10:11 schrieb Thomas Hellström (VMware):
>> [CAUTION: External Email]
>>
>> From: Thomas Hellstrom <thellstrom at vmware.com>
>>
>> With SEV encryption, all DMA memory must be marked decrypted
>> (AKA "shared") for devices to be able to read it. In the future we might
>> want to be able to switch normal (encrypted) memory to decrypted in exactly
>> the same way as we handle caching states, and that would require additional
>> memory pools. But for now, rely on memory allocated with
>> dma_alloc_coherent() which is already decrypted with SEV enabled. Set up
>> the page protection accordingly. Drivers must detect SEV enabled and switch
>> to the dma page pool.
>>
>> This patch has not yet been tested. As a follow-up, we might want to
>> cache decrypted pages in the dma page pool regardless of their caching
>> state.
> This patch is unnecessary, SEV support already works fine with at least
> amdgpu and I would expect that it also works with other drivers as well.
>
> Also see this patch:
>
> commit 64e1f830ea5b3516a4256ed1c504a265d7f2a65c
> Author: Christian König <christian.koenig at amd.com>
> Date:   Wed Mar 13 10:11:19 2019 +0100
>
>       drm: fallback to dma_alloc_coherent when memory encryption is active
>
>       We can't just map any randome page we get when memory encryption is
>       active.
>
>       Signed-off-by: Christian König <christian.koenig at amd.com>
>       Acked-by: Alex Deucher <alexander.deucher at amd.com>
>       Link: https://patchwork.kernel.org/patch/10850833/
>
> Regards,
> Christian.

Yes, I noticed that. Although I fail to see where we automagically clear 
the PTE encrypted bit when mapping coherent memory? For the linear 
kernel map, that's done within dma_alloc_coherent() but for kernel vmaps 
and and user-space maps? Is that done automatically by the x86 platform 
layer?

/Thomas


>
>> Cc: Christian König <christian.koenig at amd.com>
>> Signed-off-by: Thomas Hellstrom <thellstrom at vmware.com>
>> ---
>>    drivers/gpu/drm/ttm/ttm_bo_util.c        | 17 +++++++++++++----
>>    drivers/gpu/drm/ttm/ttm_bo_vm.c          |  6 ++++--
>>    drivers/gpu/drm/ttm/ttm_page_alloc_dma.c |  3 +++
>>    drivers/gpu/drm/vmwgfx/vmwgfx_blit.c     |  6 ++++--
>>    include/drm/ttm/ttm_bo_driver.h          |  8 +++++---
>>    include/drm/ttm/ttm_tt.h                 |  1 +
>>    6 files changed, 30 insertions(+), 11 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/ttm/ttm_bo_util.c b/drivers/gpu/drm/ttm/ttm_bo_util.c
>> index 895d77d799e4..1d6643bd0b01 100644
>> --- a/drivers/gpu/drm/ttm/ttm_bo_util.c
>> +++ b/drivers/gpu/drm/ttm/ttm_bo_util.c
>> @@ -419,11 +419,13 @@ int ttm_bo_move_memcpy(struct ttm_buffer_object *bo,
>>                   page = i * dir + add;
>>                   if (old_iomap == NULL) {
>>                           pgprot_t prot = ttm_io_prot(old_mem->placement,
>> +                                                   ttm->page_flags,
>>                                                       PAGE_KERNEL);
>>                           ret = ttm_copy_ttm_io_page(ttm, new_iomap, page,
>>                                                      prot);
>>                   } else if (new_iomap == NULL) {
>>                           pgprot_t prot = ttm_io_prot(new_mem->placement,
>> +                                                   ttm->page_flags,
>>                                                       PAGE_KERNEL);
>>                           ret = ttm_copy_io_ttm_page(ttm, old_iomap, page,
>>                                                      prot);
>> @@ -526,11 +528,11 @@ static int ttm_buffer_object_transfer(struct ttm_buffer_object *bo,
>>           return 0;
>>    }
>>
>> -pgprot_t ttm_io_prot(uint32_t caching_flags, pgprot_t tmp)
>> +pgprot_t ttm_io_prot(u32 caching_flags, u32 tt_page_flags, pgprot_t tmp)
>>    {
>>           /* Cached mappings need no adjustment */
>>           if (caching_flags & TTM_PL_FLAG_CACHED)
>> -               return tmp;
>> +               goto check_encryption;
>>
>>    #if defined(__i386__) || defined(__x86_64__)
>>           if (caching_flags & TTM_PL_FLAG_WC)
>> @@ -548,6 +550,11 @@ pgprot_t ttm_io_prot(uint32_t caching_flags, pgprot_t tmp)
>>    #if defined(__sparc__) || defined(__mips__)
>>           tmp = pgprot_noncached(tmp);
>>    #endif
>> +
>> +check_encryption:
>> +       if (tt_page_flags & TTM_PAGE_FLAG_DECRYPTED)
>> +               tmp = pgprot_decrypted(tmp);
>> +
>>           return tmp;
>>    }
>>    EXPORT_SYMBOL(ttm_io_prot);
>> @@ -594,7 +601,8 @@ static int ttm_bo_kmap_ttm(struct ttm_buffer_object *bo,
>>           if (ret)
>>                   return ret;
>>
>> -       if (num_pages == 1 && (mem->placement & TTM_PL_FLAG_CACHED)) {
>> +       if (num_pages == 1 && (mem->placement & TTM_PL_FLAG_CACHED) &&
>> +           !(ttm->page_flags & TTM_PAGE_FLAG_DECRYPTED)) {
>>                   /*
>>                    * We're mapping a single page, and the desired
>>                    * page protection is consistent with the bo.
>> @@ -608,7 +616,8 @@ static int ttm_bo_kmap_ttm(struct ttm_buffer_object *bo,
>>                    * We need to use vmap to get the desired page protection
>>                    * or to make the buffer object look contiguous.
>>                    */
>> -               prot = ttm_io_prot(mem->placement, PAGE_KERNEL);
>> +               prot = ttm_io_prot(mem->placement, ttm->page_flags,
>> +                                  PAGE_KERNEL);
>>                   map->bo_kmap_type = ttm_bo_map_vmap;
>>                   map->virtual = vmap(ttm->pages + start_page, num_pages,
>>                                       0, prot);
>> diff --git a/drivers/gpu/drm/ttm/ttm_bo_vm.c b/drivers/gpu/drm/ttm/ttm_bo_vm.c
>> index 2d9862fcf6fd..e12247edd243 100644
>> --- a/drivers/gpu/drm/ttm/ttm_bo_vm.c
>> +++ b/drivers/gpu/drm/ttm/ttm_bo_vm.c
>> @@ -245,7 +245,6 @@ vm_fault_t ttm_bo_vm_fault_reserved(struct vm_fault *vmf,
>>                   goto out_io_unlock;
>>           }
>>
>> -       cvma.vm_page_prot = ttm_io_prot(bo->mem.placement, prot);
>>           if (!bo->mem.bus.is_iomem) {
>>                   struct ttm_operation_ctx ctx = {
>>                           .interruptible = false,
>> @@ -255,13 +254,16 @@ vm_fault_t ttm_bo_vm_fault_reserved(struct vm_fault *vmf,
>>                   };
>>
>>                   ttm = bo->ttm;
>> +               cvma.vm_page_prot = ttm_io_prot(bo->mem.placement,
>> +                                               ttm->page_flags, prot);
>>                   if (ttm_tt_populate(bo->ttm, &ctx)) {
>>                           ret = VM_FAULT_OOM;
>>                           goto out_io_unlock;
>>                   }
>>           } else {
>>                   /* Iomem should not be marked encrypted */
>> -               cvma.vm_page_prot = pgprot_decrypted(cvma.vm_page_prot);
>> +               cvma.vm_page_prot = ttm_io_prot(bo->mem.placement,
>> +                                               TTM_PAGE_FLAG_DECRYPTED, prot);
>>           }
>>
>>           /*
>> diff --git a/drivers/gpu/drm/ttm/ttm_page_alloc_dma.c b/drivers/gpu/drm/ttm/ttm_page_alloc_dma.c
>> index 98d100fd1599..1a8a09c05805 100644
>> --- a/drivers/gpu/drm/ttm/ttm_page_alloc_dma.c
>> +++ b/drivers/gpu/drm/ttm/ttm_page_alloc_dma.c
>> @@ -979,6 +979,9 @@ int ttm_dma_populate(struct ttm_dma_tt *ttm_dma, struct device *dev,
>>           }
>>
>>           ttm->state = tt_unbound;
>> +       if (sev_active())
>> +               ttm->page_flags |= TTM_PAGE_FLAG_DECRYPTED;
>> +
>>           return 0;
>>    }
>>    EXPORT_SYMBOL_GPL(ttm_dma_populate);
>> diff --git a/drivers/gpu/drm/vmwgfx/vmwgfx_blit.c b/drivers/gpu/drm/vmwgfx/vmwgfx_blit.c
>> index fc6673cde289..11c8cd248530 100644
>> --- a/drivers/gpu/drm/vmwgfx/vmwgfx_blit.c
>> +++ b/drivers/gpu/drm/vmwgfx/vmwgfx_blit.c
>> @@ -483,8 +483,10 @@ int vmw_bo_cpu_blit(struct ttm_buffer_object *dst,
>>           d.src_pages = src->ttm->pages;
>>           d.dst_num_pages = dst->num_pages;
>>           d.src_num_pages = src->num_pages;
>> -       d.dst_prot = ttm_io_prot(dst->mem.placement, PAGE_KERNEL);
>> -       d.src_prot = ttm_io_prot(src->mem.placement, PAGE_KERNEL);
>> +       d.dst_prot = ttm_io_prot(dst->mem.placement, dst->ttm->page_flags,
>> +                                PAGE_KERNEL);
>> +       d.src_prot = ttm_io_prot(src->mem.placement, src->ttm->page_flags,
>> +                                PAGE_KERNEL);
>>           d.diff = diff;
>>
>>           for (j = 0; j < h; ++j) {
>> diff --git a/include/drm/ttm/ttm_bo_driver.h b/include/drm/ttm/ttm_bo_driver.h
>> index 53fe95be5b32..261cc89c024e 100644
>> --- a/include/drm/ttm/ttm_bo_driver.h
>> +++ b/include/drm/ttm/ttm_bo_driver.h
>> @@ -889,13 +889,15 @@ int ttm_bo_pipeline_gutting(struct ttm_buffer_object *bo);
>>    /**
>>     * ttm_io_prot
>>     *
>> - * @c_state: Caching state.
>> + * @caching_flags: The caching flags of the map.
>> + * @tt_page_flags: The tt_page_flags of the map, TTM_PAGE_FLAG_*
>>     * @tmp: Page protection flag for a normal, cached mapping.
>>     *
>>     * Utility function that returns the pgprot_t that should be used for
>> - * setting up a PTE with the caching model indicated by @c_state.
>> + * setting up a PTE with the caching model indicated by @caching_flags,
>> + * and encryption state indicated by @tt_page_flags,
>>     */
>> -pgprot_t ttm_io_prot(uint32_t caching_flags, pgprot_t tmp);
>> +pgprot_t ttm_io_prot(u32 caching_flags, u32 tt_page_flags, pgprot_t tmp);
>>
>>    extern const struct ttm_mem_type_manager_func ttm_bo_manager_func;
>>
>> diff --git a/include/drm/ttm/ttm_tt.h b/include/drm/ttm/ttm_tt.h
>> index c0e928abf592..45cc26355513 100644
>> --- a/include/drm/ttm/ttm_tt.h
>> +++ b/include/drm/ttm/ttm_tt.h
>> @@ -41,6 +41,7 @@ struct ttm_operation_ctx;
>>    #define TTM_PAGE_FLAG_DMA32           (1 << 7)
>>    #define TTM_PAGE_FLAG_SG              (1 << 8)
>>    #define TTM_PAGE_FLAG_NO_RETRY       (1 << 9)
>> +#define TTM_PAGE_FLAG_DECRYPTED       (1 << 10)
>>
>>    enum ttm_caching_state {
>>           tt_uncached,
>> --
>> 2.20.1
>>



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