drm/nouveau: verify that hardware supports the flush page address

Ensure that the DMA address of the framebuffer flush page is not larger
than its hardware register.

On GPUs older than Hopper, the register for the address can hold up to a
40-bit address (right-shifted by 8 so that it fits in the 32-bit
register), and on Hopper and later it can be 52 bits (64-bit register
where bits 52-63 must be zero).

Recently it was discovered that under certain conditions, the flush page
could be allocated outside this range.  Although this bug was fixed, we
can ensure that any future changes to this code don't accidentally
generate an invalid page address.

Signed-off-by: Timur Tabi <ttabi@nvidia.com>
Reviewed-by: Lyude Paul <lyude@redhat.com>
Signed-off-by: Lyude Paul <lyude@redhat.com>
Link: https://patch.msgid.link/20251113230323.1271726-2-ttabi@nvidia.com

Author: ttabi

drivers/gpu/drm/nouveau/nvkm/subdev/fb/gb100.c

@@ -15,6 +15,9 @@ gb100_fb_sysmem_flush_page_init(struct nvkm_fb *fb)
 	const u32 hshub = DRF_LO(NV_PFB_HSHUB0);
 	struct nvkm_device *device = fb->subdev.device;
 
+	// Ensure that the address is within hardware limits
+	WARN_ON(fb->sysmem.flush_page_addr > DMA_BIT_MASK(52));
+
 	nvkm_wr32(device, hshub + NV_PFB_HSHUB_PCIE_FLUSH_SYSMEM_ADDR_HI, addr_hi);
 	nvkm_wr32(device, hshub + NV_PFB_HSHUB_PCIE_FLUSH_SYSMEM_ADDR_LO, addr_lo);
 	nvkm_wr32(device, hshub + NV_PFB_HSHUB_EG_PCIE_FLUSH_SYSMEM_ADDR_HI, addr_hi);

drivers/gpu/drm/nouveau/nvkm/subdev/fb/gb202.c

@@ -13,6 +13,9 @@ gb202_fb_sysmem_flush_page_init(struct nvkm_fb *fb)
 	struct nvkm_device *device = fb->subdev.device;
 	const u64 addr = fb->sysmem.flush_page_addr;
 
+	// Ensure that the address is within hardware limits
+	WARN_ON(fb->sysmem.flush_page_addr > DMA_BIT_MASK(52));
+
 	nvkm_wr32(device, NV_PFB_FBHUB0_PCIE_FLUSH_SYSMEM_ADDR_HI, upper_32_bits(addr));
 	nvkm_wr32(device, NV_PFB_FBHUB0_PCIE_FLUSH_SYSMEM_ADDR_LO, lower_32_bits(addr));
 }

drivers/gpu/drm/nouveau/nvkm/subdev/fb/gf100.c

@@ -80,6 +80,9 @@ gf100_fb_init_page(struct nvkm_fb *fb)
 void
 gf100_fb_sysmem_flush_page_init(struct nvkm_fb *fb)
 {
+	// Ensure that the address can actually fit in the register
+	WARN_ON(fb->sysmem.flush_page_addr > DMA_BIT_MASK(40));
+
 	nvkm_wr32(fb->subdev.device, 0x100c10, fb->sysmem.flush_page_addr >> 8);
 }
 

drivers/gpu/drm/nouveau/nvkm/subdev/fb/gh100.c

@@ -13,6 +13,9 @@ gh100_fb_sysmem_flush_page_init(struct nvkm_fb *fb)
 	const u64 addr = fb->sysmem.flush_page_addr >> NV_PFB_NISO_FLUSH_SYSMEM_ADDR_SHIFT;
 	struct nvkm_device *device = fb->subdev.device;
 
+	// Ensure that the address is within hardware limits
+	WARN_ON(fb->sysmem.flush_page_addr > DMA_BIT_MASK(52));
+
 	nvkm_wr32(device, NV_PFB_FBHUB_PCIE_FLUSH_SYSMEM_ADDR_HI, upper_32_bits(addr));
 	nvkm_wr32(device, NV_PFB_FBHUB_PCIE_FLUSH_SYSMEM_ADDR_LO, lower_32_bits(addr));
 }

drivers/gpu/drm/nouveau/nvkm/subdev/fb/nv50.c

@@ -214,6 +214,9 @@ nv50_fb_tags(struct nvkm_fb *base)
 static void
 nv50_fb_sysmem_flush_page_init(struct nvkm_fb *fb)
 {
+	// Ensure that the address can actually fit in the register
+	WARN_ON(fb->sysmem.flush_page_addr > DMA_BIT_MASK(40));
+
 	nvkm_wr32(fb->subdev.device, 0x100c08, fb->sysmem.flush_page_addr >> 8);
 }