drm/ttm: Make sure the mapped tt pages are decrypted when needed

commit 71ce046327cfd3aef3f93d1c44e091395eb03f8f upstream.

Some drivers require the mapped tt pages to be decrypted. In an ideal
world this would have been handled by the dma layer, but the TTM page
fault handling would have to be rewritten to able to do that.

A side-effect of the TTM page fault handling is using a dma allocation
per order (via ttm_pool_alloc_page) which makes it impossible to just
trivially use dma_mmap_attrs. As a result ttm has to be very careful
about trying to make its pgprot for the mapped tt pages match what
the dma layer thinks it is. At the ttm layer it's possible to
deduce the requirement to have tt pages decrypted by checking
whether coherent dma allocations have been requested and the system
is running with confidential computing technologies.

This approach isn't ideal but keeping TTM matching DMAs expectations
for the page properties is in general fragile, unfortunately proper
fix would require a rewrite of TTM's page fault handling.

Fixes vmwgfx with SEV enabled.

v2: Explicitly include cc_platform.h
v3: Use CC_ATTR_GUEST_MEM_ENCRYPT instead of CC_ATTR_MEM_ENCRYPT to
limit the scope to guests and log when memory decryption is enabled.

Signed-off-by: Zack Rusin <zack.rusin@broadcom.com>
Fixes: 3bf3710e3718 ("drm/ttm: Add a generic TTM memcpy move for page-based iomem")
Reviewed-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Acked-by: Christian König <christian.koenig@amd.com>
Cc: Huang Rui <ray.huang@amd.com>
Cc: dri-devel@lists.freedesktop.org
Cc: linux-kernel@vger.kernel.org
Cc: <stable@vger.kernel.org> # v5.14+
Link: https://patchwork.freedesktop.org/patch/msgid/20230926040359.3040017-1-zack@kde.org
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Ye Li <ye.li@broadcom.com>
Signed-off-by: Ajay Kaher <ajay.kaher@broadcom.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/gpu/drm/ttm/ttm_bo_util.c b/drivers/gpu/drm/ttm/ttm_bo_util.c
index fa04e62202c15778832b010db85a5f755c2c3c81..dcb2c23dc6de4d7db88df4f4bacaff3c0f228d1e 100644 (file)
--- a/drivers/gpu/drm/ttm/ttm_bo_util.c
+++ b/drivers/gpu/drm/ttm/ttm_bo_util.c
@@ -274,7 +274,13 @@ pgprot_t ttm_io_prot(struct ttm_buffer_object *bo, struct ttm_resource *res,
        enum ttm_caching caching;
 
        man = ttm_manager_type(bo->bdev, res->mem_type);
-       caching = man->use_tt ? bo->ttm->caching : res->bus.caching;
+       if (man->use_tt) {
+               caching = bo->ttm->caching;
+               if (bo->ttm->page_flags & TTM_TT_FLAG_DECRYPTED)
+                       tmp = pgprot_decrypted(tmp);
+       } else  {
+               caching = res->bus.caching;
+       }
 
        return ttm_prot_from_caching(caching, tmp);
 }
@@ -317,6 +323,8 @@ static int ttm_bo_kmap_ttm(struct ttm_buffer_object *bo,
                .no_wait_gpu = false
        };
        struct ttm_tt *ttm = bo->ttm;
+       struct ttm_resource_manager *man =
+                       ttm_manager_type(bo->bdev, bo->resource->mem_type);
        pgprot_t prot;
        int ret;
 
@@ -326,7 +334,8 @@ static int ttm_bo_kmap_ttm(struct ttm_buffer_object *bo,
        if (ret)
                return ret;
 
-       if (num_pages == 1 && ttm->caching == ttm_cached) {
+       if (num_pages == 1 && ttm->caching == ttm_cached &&
+           !(man->use_tt && (ttm->page_flags & TTM_TT_FLAG_DECRYPTED))) {
                /*
                 * We're mapping a single page, and the desired
                 * page protection is consistent with the bo.

diff --git a/drivers/gpu/drm/ttm/ttm_tt.c b/drivers/gpu/drm/ttm/ttm_tt.c
index d505603930a79af28aca8188e596590311b857c3..91e179701571e52c8319b392ef6f6c282516a29b 100644 (file)
--- a/drivers/gpu/drm/ttm/ttm_tt.c
+++ b/drivers/gpu/drm/ttm/ttm_tt.c
@@ -31,11 +31,13 @@
 
 #define pr_fmt(fmt) "[TTM] " fmt
 
+#include <linux/cc_platform.h>
 #include <linux/sched.h>
 #include <linux/shmem_fs.h>
 #include <linux/file.h>
 #include <linux/module.h>
 #include <drm/drm_cache.h>
+#include <drm/drm_device.h>
 #include <drm/ttm/ttm_bo_driver.h>
 
 #include "ttm_module.h"
@@ -59,6 +61,7 @@ static atomic_long_t ttm_dma32_pages_allocated;
 int ttm_tt_create(struct ttm_buffer_object *bo, bool zero_alloc)
 {
        struct ttm_device *bdev = bo->bdev;
+       struct drm_device *ddev = bo->base.dev;
        uint32_t page_flags = 0;
 
        dma_resv_assert_held(bo->base.resv);
@@ -80,6 +83,15 @@ int ttm_tt_create(struct ttm_buffer_object *bo, bool zero_alloc)
                pr_err("Illegal buffer object type\n");
                return -EINVAL;
        }
+       /*
+        * When using dma_alloc_coherent with memory encryption the
+        * mapped TT pages need to be decrypted or otherwise the drivers
+        * will end up sending encrypted mem to the gpu.
+        */
+       if (bdev->pool.use_dma_alloc && cc_platform_has(CC_ATTR_GUEST_MEM_ENCRYPT)) {
+               page_flags |= TTM_TT_FLAG_DECRYPTED;
+               drm_info(ddev, "TT memory decryption enabled.");
+       }
 
        bo->ttm = bdev->funcs->ttm_tt_create(bo, page_flags);
        if (unlikely(bo->ttm == NULL))

diff --git a/include/drm/ttm/ttm_tt.h b/include/drm/ttm/ttm_tt.h
index b7d3f3843f1e6fb85393c694330ee8add0a5ce14..9cbdf8ce8a051f1970c2a0fb596eb4b40bdf9a14 100644 (file)
--- a/include/drm/ttm/ttm_tt.h
+++ b/include/drm/ttm/ttm_tt.h
@@ -79,6 +79,12 @@ struct ttm_tt {
         *   page_flags = TTM_TT_FLAG_EXTERNAL |
         *                TTM_TT_FLAG_EXTERNAL_MAPPABLE;
         *
+        * TTM_TT_FLAG_DECRYPTED: The mapped ttm pages should be marked as
+        * not encrypted. The framework will try to match what the dma layer
+        * is doing, but note that it is a little fragile because ttm page
+        * fault handling abuses the DMA api a bit and dma_map_attrs can't be
+        * used to assure pgprot always matches.
+        *
         * TTM_TT_FLAG_PRIV_POPULATED: TTM internal only. DO NOT USE. This is
         * set by TTM after ttm_tt_populate() has successfully returned, and is
         * then unset when TTM calls ttm_tt_unpopulate().
@@ -87,6 +93,7 @@ struct ttm_tt {
 #define TTM_TT_FLAG_ZERO_ALLOC         (1 << 1)
 #define TTM_TT_FLAG_EXTERNAL           (1 << 2)
 #define TTM_TT_FLAG_EXTERNAL_MAPPABLE  (1 << 3)
+#define TTM_TT_FLAG_DECRYPTED          (1 << 4)
 
 #define TTM_TT_FLAG_PRIV_POPULATED  (1U << 31)
        uint32_t page_flags;