Index: sys/arch/amd64/amd64/bus_dma.c
===================================================================
RCS file: /mount/openbsd/cvs/src/sys/arch/amd64/amd64/bus_dma.c,v
diff -u -p -u -p -r1.51 bus_dma.c
--- sys/arch/amd64/amd64/bus_dma.c	9 Jun 2019 12:52:04 -0000	1.51
+++ sys/arch/amd64/amd64/bus_dma.c	14 Aug 2024 16:35:29 -0000
@@ -108,8 +108,13 @@ _bus_dmamap_create(bus_dma_tag_t t, bus_
     bus_size_t maxsegsz, bus_size_t boundary, int flags, bus_dmamap_t *dmamp)
 {
 	struct bus_dmamap *map;
+	struct pglist mlist;
+	struct vm_page **pg, *pgnext;
+	size_t mapsize, sz, ssize;
+	vaddr_t va, sva;
 	void *mapstore;
-	size_t mapsize;
+	int npages, error;
+	const struct kmem_dyn_mode *kd;
 
 	/*
 	 * Allocate and initialize the DMA map.  The end of the map
@@ -125,6 +130,16 @@ _bus_dmamap_create(bus_dma_tag_t t, bus_
 	 */
 	mapsize = sizeof(struct bus_dmamap) +
 	    (sizeof(bus_dma_segment_t) * (nsegments - 1));
+
+	/* allocate and use bounce buffers when running as SEV guest */
+	if (cpu_sev_guestmode) {
+		/* this many pages plus one in case we get split */
+		npages = round_page(size) / PAGE_SIZE + 1;
+		if (npages < nsegments)
+			npages = nsegments;
+		mapsize += sizeof(struct vm_page *) * npages;
+	}
+
 	if ((mapstore = malloc(mapsize, M_DEVBUF,
 	    (flags & BUS_DMA_NOWAIT) ?
 	        (M_NOWAIT|M_ZERO) : (M_WAITOK|M_ZERO))) == NULL)
@@ -135,8 +150,59 @@ _bus_dmamap_create(bus_dma_tag_t t, bus_
 	map->_dm_segcnt = nsegments;
 	map->_dm_maxsegsz = maxsegsz;
 	map->_dm_boundary = boundary;
+	if (cpu_sev_guestmode) {
+		map->_dm_pages = (void *)&map->dm_segs[nsegments];
+		map->_dm_npages = npages;
+	}
 	map->_dm_flags = flags & ~(BUS_DMA_WAITOK|BUS_DMA_NOWAIT);
 
+	if (!cpu_sev_guestmode) {
+		*dmamp = map;
+		return (0);
+	}
+
+	sz = npages << PGSHIFT;
+	kd = flags & BUS_DMA_NOWAIT ? &kd_trylock : &kd_waitok;
+	va = (vaddr_t)km_alloc(sz, &kv_any, &kp_none, kd);
+	if (va == 0) {
+		map->_dm_npages = 0;
+		free(map, M_DEVBUF, mapsize);
+		return (ENOMEM);
+	}
+
+	TAILQ_INIT(&mlist);
+	error = uvm_pglistalloc(sz, 0, -1, PAGE_SIZE, 0, &mlist, nsegments,
+	    (flags & BUS_DMA_NOWAIT) ? UVM_PLA_NOWAIT : UVM_PLA_WAITOK);
+	if (error) {
+		map->_dm_npages = 0;
+		km_free((void *)va, sz, &kv_any, &kp_none);
+		free(map, M_DEVBUF, mapsize);
+		return (ENOMEM);
+	}
+
+	sva = va;
+	ssize = sz;
+	pgnext = TAILQ_FIRST(&mlist);
+	for (pg = map->_dm_pages; npages--; va += PAGE_SIZE, pg++) {
+		*pg = pgnext;
+		error = pmap_enter(pmap_kernel(), va, VM_PAGE_TO_PHYS(*pg),
+		    PROT_READ | PROT_WRITE,
+		    PROT_READ | PROT_WRITE | PMAP_WIRED |
+		    PMAP_CANFAIL | PMAP_NOCRYPT);
+		if (error) {
+			pmap_update(pmap_kernel());
+			map->_dm_npages = 0;
+			km_free((void *)sva, ssize, &kv_any, &kp_none);
+			free(map, M_DEVBUF, mapsize);
+			uvm_pglistfree(&mlist);
+			return (ENOMEM);
+		}
+		pgnext = TAILQ_NEXT(*pg, pageq);
+		bzero((void *)va, PAGE_SIZE);
+	}
+	pmap_update(pmap_kernel());
+	map->_dm_pgva = sva;
+
 	*dmamp = map;
 	return (0);
 }
@@ -149,7 +215,22 @@ void
 _bus_dmamap_destroy(bus_dma_tag_t t, bus_dmamap_t map)
 {
 	size_t mapsize;
-	
+	struct vm_page **pg;
+	struct pglist mlist;
+
+	if (map->_dm_pgva) {
+		km_free((void *)map->_dm_pgva, map->_dm_npages << PGSHIFT,
+		    &kv_any, &kp_none);
+	}
+
+	if (map->_dm_pages) {
+		TAILQ_INIT(&mlist);
+		for (pg = map->_dm_pages; map->_dm_npages--; pg++) {
+			TAILQ_INSERT_TAIL(&mlist, *pg, pageq);
+		}
+		uvm_pglistfree(&mlist);
+	}
+
 	mapsize = sizeof(struct bus_dmamap) +
 		(sizeof(bus_dma_segment_t) * (map->_dm_segcnt - 1));
 	free(map, M_DEVBUF, mapsize);
@@ -383,6 +464,7 @@ _bus_dmamap_unload(bus_dma_tag_t t, bus_
 	 */
 	map->dm_mapsize = 0;
 	map->dm_nsegs = 0;
+	map->_dm_nused = 0;
 }
 
 /*
@@ -393,7 +475,40 @@ void
 _bus_dmamap_sync(bus_dma_tag_t t, bus_dmamap_t map, bus_addr_t addr,
     bus_size_t size, int op)
 {
-	/* Nothing to do here. */
+	bus_dma_segment_t *sg;
+	int i, off = addr;
+	bus_size_t l;
+
+	if (!cpu_sev_guestmode)
+		return;
+
+	for (i = map->_dm_segcnt, sg = map->dm_segs; size && i--; sg++) {
+		if (off >= sg->ds_len) {
+			off -= sg->ds_len;
+			continue;
+		}
+
+		l = sg->ds_len - off;
+		if (l > size)
+			l = size;
+		size -= l;
+
+		/* PREREAD and POSTWRITE are no-ops. */
+
+		/* READ: device -> memory */
+		if (op & BUS_DMASYNC_POSTREAD) {
+			bcopy((void *)(sg->_ds_bounce_va + off),
+			    (void *)(sg->_ds_va + off), l);
+		}
+
+		/* WRITE: memory -> device */
+		if (op & BUS_DMASYNC_PREWRITE) {
+			bcopy((void *)(sg->_ds_va + off),
+			    (void *)(sg->_ds_bounce_va + off), l);
+		}
+
+		off = 0;
+	}
 }
 
 /*
@@ -566,9 +681,10 @@ _bus_dmamap_load_buffer(bus_dma_tag_t t,
 {
 	bus_size_t sgsize;
 	bus_addr_t curaddr, lastaddr, baddr, bmask;
-	vaddr_t vaddr = (vaddr_t)buf;
-	int seg;
+	vaddr_t pgva = -1, vaddr = (vaddr_t)buf;
+	int seg, page, off;
 	pmap_t pmap;
+	struct vm_page *pg;
 
 	if (p != NULL)
 		pmap = p->p_vmspace->vm_map.pmap;
@@ -589,6 +705,18 @@ _bus_dmamap_load_buffer(bus_dma_tag_t t,
 			panic("Non dma-reachable buffer at curaddr %#lx(raw)",
 			    curaddr);
 
+		if (cpu_sev_guestmode) {
+			/* use bounce buffer */
+			if (map->_dm_nused + 1 >= map->_dm_npages)
+				return (ENOMEM);
+
+			off = vaddr & PAGE_MASK;
+			pg = map->_dm_pages[page = map->_dm_nused++];
+			curaddr = VM_PAGE_TO_PHYS(pg) + off;
+
+			pgva = map->_dm_pgva + (page << PGSHIFT) + off;
+		}
+
 		/*
 		 * Compute the segment size, and adjust counts.
 		 */
@@ -612,6 +740,8 @@ _bus_dmamap_load_buffer(bus_dma_tag_t t,
 		if (first) {
 			map->dm_segs[seg].ds_addr = curaddr;
 			map->dm_segs[seg].ds_len = sgsize;
+			map->dm_segs[seg]._ds_va = vaddr;
+			map->dm_segs[seg]._ds_bounce_va = pgva;
 			first = 0;
 		} else {
 			if (curaddr == lastaddr &&
@@ -626,6 +756,8 @@ _bus_dmamap_load_buffer(bus_dma_tag_t t,
 					break;
 				map->dm_segs[seg].ds_addr = curaddr;
 				map->dm_segs[seg].ds_len = sgsize;
+				map->dm_segs[seg]._ds_va = vaddr;
+				map->dm_segs[seg]._ds_bounce_va = pgva;
 			}
 		}
 
Index: sys/arch/amd64/include/bus.h
===================================================================
RCS file: /mount/openbsd/cvs/src/sys/arch/amd64/include/bus.h,v
diff -u -p -u -p -r1.35 bus.h
--- sys/arch/amd64/include/bus.h	28 Oct 2020 09:58:57 -0000	1.35
+++ sys/arch/amd64/include/bus.h	14 Aug 2024 16:35:29 -0000
@@ -552,6 +552,9 @@ typedef struct bus_dmamap		*bus_dmamap_t
 struct bus_dma_segment {
 	bus_addr_t	ds_addr;	/* DMA address */
 	bus_size_t	ds_len;		/* length of transfer */
+	vaddr_t		_ds_va;		/* mapped loaded data */
+	vaddr_t		_ds_bounce_va;	/* mapped bounced data */
+
 	/*
 	 * Ugh. need this so can pass alignment down from bus_dmamem_alloc
 	 * to scatter gather maps. only the first one is used so the rest is
@@ -654,6 +657,11 @@ struct bus_dmamap {
 	bus_size_t	_dm_boundary;	/* don't cross this */
 
 	void		*_dm_cookie;	/* cookie for bus-specific functions */
+
+	struct vm_page **_dm_pages;	/* replacement pages */
+	vaddr_t		_dm_pgva;	/* those above -- mapped */
+	int		_dm_npages;	/* number of pages allocated */
+	int		_dm_nused;	/* number of pages replaced */
 
 	/*
 	 * PUBLIC MEMBERS: these are used by machine-independent code.