diff --git a/sys/src/9/pc/vgaigfx.c b/sys/src/9/pc/vgaigfx.c
index c0f3037b3..baaee2564 100644
--- a/sys/src/9/pc/vgaigfx.c
+++ b/sys/src/9/pc/vgaigfx.c
@@ -12,72 +12,24 @@
 #include <cursor.h>
 #include "screen.h"
 
-static ulong
-stolenmb(Pcidev *p)
-{
-	switch(p->did){
-	case 0x0412:	/* Haswell HD Graphics 4600 */
-	case 0x0a16:	/* Haswell HD Graphics 4400 */
-	case 0x0126:	/* Sandy Bridge HD Graphics 3000 */
-	case 0x0166:	/* Ivy Bridge */
-	case 0x0102:	/* Core-5 Sandy Bridge */
-	case 0x0152:	/* Core-i3 */
-		switch((pcicfgr16(p, 0x50) >> 3) & 0x1f){
-		case 0x01:	return 32  - 2;
-		case 0x02:	return 64  - 2;		/* 0102 Dell machine here */
-		case 0x03:	return 96  - 2;
-		case 0x04:	return 128 - 2;
-		case 0x05:	return 32  - 2;
-		case 0x06:	return 48  - 2;
-		case 0x07:	return 64  - 2;
-		case 0x08:	return 128 - 2;
-		case 0x09:	return 256 - 2;
-		case 0x0A:	return 96  - 2;
-		case 0x0B:	return 160 - 2;
-		case 0x0C:	return 224 - 2;
-		case 0x0D:	return 352 - 2;
-		case 0x0E:	return 448 - 2;
-		case 0x0F:	return 480 - 2;
-		case 0x10:	return 512 - 2;
-		}
-		break;
-	case 0x2a42:	/* X200 */
-	case 0x29a2:	/* 82P965/G965 HECI desktop */
-	case 0x2a02:	/* CF-R7 */
-		switch((pcicfgr16(p, 0x52) >> 4) & 7){
-		case 0x01:	return 1;
-		case 0x02:	return 4;
-		case 0x03:	return 8;
-		case 0x04:	return 16;
-		case 0x05:	return 32;
-		case 0x06:	return 48;
-		case 0x07:	return 64;
-		}
-		break;
-	}
-	return 0;
-}
-
 static uintptr
-gmsize(Pcidev *pci, void *mmio)
+igfxcuralloc(Pcidev *pci, void *mmio, int apsize)
 {
-	u32int x, i, npg, *gtt;
+	int n;
+	u32int pa, *buf, *p, *e;
 
-	npg = stolenmb(pci)<<(20-12);
-	if(npg == 0)
+	buf = mallocalign(64*64*4, BY2PG, 0, 0);
+	if(buf == nil){
+		print("igfx: no memory for cursor image\n");
 		return 0;
-	gtt = (u32int*)((uchar*)mmio + pci->mem[0].size/2);
-	if((gtt[0]&1) == 0)
-		return 0;
-	x = (gtt[0]>>12)+1;
-	for(i=1; i<npg; i++){
-		if((gtt[i]&1) == 0 || (gtt[i]>>12) != x)
-			break;
-		x++;
 	}
-	if(0) print("igfx: graphics memory at %p-%p (%ud MB)\n", 
-		(uintptr)(x-i)<<12, (uintptr)x<<12, (i>>(20-12)));
-	return (uintptr)i<<12;
+	n = (apsize > 128*MB ? 128*1024 : apsize/1024) / 4 - 4;
+	p = (u32int*)((uchar*)mmio + pci->mem[0].size/2) + n;
+	*(u32int*)((uchar*)mmio + 0x2170) = 0;	/* flush write buffers */
+	for(e=p+4, pa=PADDR(buf); p<e; p++, pa+=1<<12)
+		*p = pa | 1;
+	*(u32int*)((uchar*)mmio + 0x2170) = 0;	/* flush write buffers */
+	return (uintptr)n << 12;
 }
 
 static void
@@ -98,13 +50,7 @@ igfxenable(VGAscr* scr)
 		vgalinearpci(scr);
 	if(scr->apsize){
 		addvgaseg("igfxscreen", scr->paddr, scr->apsize);
-		scr->storage = gmsize(p, scr->mmio);
-		if(scr->storage < MB)
-			scr->storage = 0;
-		else if(scr->storage > scr->apsize)
-			scr->storage = scr->apsize;
-		if(scr->storage != 0)
-			scr->storage -= PGROUND(64*64*4);
+		scr->storage = igfxcuralloc(p, scr->mmio, scr->apsize);
 	}
 	scr->softscreen = 1;
 }
diff --git a/sys/src/cmd/aux/vga/igfx.c b/sys/src/cmd/aux/vga/igfx.c
index cc595c132..48a2a363e 100644
--- a/sys/src/cmd/aux/vga/igfx.c
+++ b/sys/src/cmd/aux/vga/igfx.c
@@ -1593,6 +1593,76 @@ disablepipe(Igfx *igfx, int x)
 		csr(igfx, igfx->dpllsel[0].a, 8<<(x*4), 0);
 }
 
+void
+checkgtt(Igfx *igfx, Mode *m)
+{
+	int fd, c;
+	ulong n;
+	char buf[64], *fl[5];
+	u32int i, j, pa, nilpte, *gtt;
+
+	if(igfx->mmio == nil)
+		return;
+	gtt = (u32int*)((uchar*)igfx->mmio + igfx->pci->mem[0].size/2);
+	pa = (gtt[0] & ~((1<<12)-1)) + (1<<12) | 1;
+	for(i=1; i<64*1024/4-4; i++, pa+=1<<12)
+		if((gtt[i] & ~((1<<11)-1<<1)) != pa)
+			break;
+	n = m->x * m->y * m->z / 8;
+	if(i<<12 >= n)
+		return;
+
+	/* unmap pages past stolen memory */
+	nilpte = gtt[64*1024/4-5];
+	wr(igfx, 0x2170, 0);	/* flush write buffers */
+	for(j=i; j<64*1024/4-5; j++){
+		if((gtt[j] & 1) == 0 || (gtt[j] & ~((1<<11)-1<<1)) == pa)
+			break;
+		pa = gtt[j];
+		gtt[j] = nilpte;
+	}
+	wr(igfx, 0x2170, 0);	/* flush write buffers */
+
+	trace("%s: mapping %lud additional bytes for requested mode\n", igfx->ctlr->name, n - (i<<12));
+	snprint(buf, sizeof buf, "#g/igfxtra");
+	if((fd = open(buf, OREAD)) >= 0){
+		close(fd);
+		if(remove(buf) < 0)
+			goto err;
+	}
+	if((fd = create(buf, OREAD, DMDIR|0777)) < 0)
+		goto err;
+	close(fd);
+	strncat(buf, "/ctl", sizeof(buf)-strlen("/ctl"));
+	if((fd = open(buf, ORDWR|OTRUNC)) < 0)
+		goto err;
+	snprint(buf, sizeof buf, "va 0x10000000 %#lux fixed", n - (i<<12));
+	if(write(fd, buf, strlen(buf)) < 0){
+		close(fd);
+		goto err;
+	}
+	seek(fd, 0, 0);
+	if((c = read(fd, buf, sizeof buf)) <= 0){
+		close(fd);
+		goto err;
+	}
+	close(fd);
+	buf[c-1] = 0;
+	if(getfields(buf, fl, nelem(fl), 0, " ") != nelem(fl)
+	|| (pa = strtoul(fl[4], nil, 16)) == 0){
+		werrstr("invalid physical base address");
+		goto err;
+	}
+	n >>= 12;
+	wr(igfx, 0x2170, 0);	/* flush write buffers */
+	for(; i<n; i++, pa+=1<<12)
+		gtt[i] = pa | 1;
+	wr(igfx, 0x2170, 0);	/* flush write buffers */
+	return;
+err:
+	trace("%s: checkgtt: %r\n", igfx->ctlr->name);
+}
+
 static void
 load(Vga* vga, Ctlr* ctlr)
 {
@@ -1638,6 +1708,9 @@ load(Vga* vga, Ctlr* ctlr)
 	for(x = 0; x < igfx->npipe; x++)
 		disablepipe(igfx, x);
 
+	/* check if enough memory has been mapped for requested mode */
+	checkgtt(igfx, vga->mode);
+
 	if(igfx->type == TypeG45){
 		/* toggle dsp a on and off (from enable sequence) */
 		csr(igfx, igfx->pipe[0].conf.a, 3<<18, 0);