Hi,
following the discussion about mbufs, I have some questions about 64bit
DMA in general.
Openbsd on amd64 assumes that DMA is only possible to the lower 4GB. But
there are many devices (PCIe, virtio, ...) that can do DMA to the whole
memory. Is it feasible to have known good devices opt-in into 64bit DMA?
I have done a patch that allows virtio to do 64bit DMA. This works insofar
as the queues used by the device will now be allocated above 4GB. But this
is only a small amount of memory. More interesting would be bufs and
mbufs.
For bufs, Bob added some code for copying bufs above/below 4GB. But this
code only has a single flag B_DMA to denote if DMA is possible into a buf
or not. Would it make sense to replace that by a mechanism that is device
specific, so that we can use devices efficiently that allow 64bit DMA?
Maybe a flag in the device vnode?
Does it make sense to commit something like the diff below (not tested
much), even if it saves at most a few MB below 4GB right now?
Cheers,
Stefan
diff --git sys/arch/amd64/amd64/bus_dma.c sys/arch/amd64/amd64/bus_dma.c
index 8eaa2e7..1aba7c0 100644
--- sys/arch/amd64/amd64/bus_dma.c
+++ sys/arch/amd64/amd64/bus_dma.c
@@ -293,6 +293,7 @@ _bus_dmamap_load_raw(bus_dma_tag_t t, bus_dmamap_t map,
bus_dma_segment_t *segs,
{
bus_addr_t paddr, baddr, bmask, lastaddr = 0;
bus_size_t plen, sgsize, mapsize;
+ struct uvm_constraint_range *constraint = t->_cookie;
int first = 1;
int i, seg = 0;
@@ -320,7 +321,7 @@ _bus_dmamap_load_raw(bus_dma_tag_t t, bus_dmamap_t map,
bus_dma_segment_t *segs,
if (plen < sgsize)
sgsize = plen;
- if (paddr > dma_constraint.ucr_high)
+ if (paddr > constraint->ucr_high)
panic("Non dma-reachable buffer at paddr
%#lx(raw)",
paddr);
@@ -405,15 +406,11 @@ _bus_dmamem_alloc(bus_dma_tag_t t, bus_size_t size,
bus_size_t alignment,
bus_size_t boundary, bus_dma_segment_t *segs, int nsegs, int *rsegs,
int flags)
{
+ struct uvm_constraint_range *constraint = t->_cookie;
- /*
- * XXX in the presence of decent (working) iommus and bouncebuffers
- * we can then fallback this allocation to a range of { 0, -1 }.
- * However for now we err on the side of caution and allocate dma
- * memory under the 4gig boundary.
- */
return (_bus_dmamem_alloc_range(t, size, alignment, boundary,
- segs, nsegs, rsegs, flags, (bus_addr_t)0, (bus_addr_t)0xffffffff));
+ segs, nsegs, rsegs, flags, (bus_addr_t)constraint->ucr_low,
+ (bus_addr_t)constraint->ucr_high));
}
/*
@@ -567,6 +564,7 @@ _bus_dmamap_load_buffer(bus_dma_tag_t t, bus_dmamap_t map,
void *buf,
bus_size_t sgsize;
bus_addr_t curaddr, lastaddr, baddr, bmask;
vaddr_t vaddr = (vaddr_t)buf;
+ struct uvm_constraint_range *constraint = t->_cookie;
int seg;
pmap_t pmap;
@@ -584,7 +582,7 @@ _bus_dmamap_load_buffer(bus_dma_tag_t t, bus_dmamap_t map,
void *buf,
*/
pmap_extract(pmap, vaddr, (paddr_t *)&curaddr);
- if (curaddr > dma_constraint.ucr_high)
+ if (curaddr > constraint->ucr_high)
panic("Non dma-reachable buffer at curaddr %#lx(raw)",
curaddr);
diff --git sys/arch/amd64/amd64/machdep.c sys/arch/amd64/amd64/machdep.c
index de9f481..7640532 100644
--- sys/arch/amd64/amd64/machdep.c
+++ sys/arch/amd64/amd64/machdep.c
@@ -201,6 +201,12 @@ struct vm_map *phys_map = NULL;
/* UVM constraint ranges. */
struct uvm_constraint_range isa_constraint = { 0x0, 0x00ffffffUL };
+ /*
+ * XXX in the presence of decent (working) iommus and bouncebuffers
+ * we can then fallback this allocation to a range of { 0, -1 }.
+ * However for now we err on the side of caution and allocate dma
+ * memory under the 4gig boundary.
+ */
struct uvm_constraint_range dma_constraint = { 0x0, 0xffffffffUL };
struct uvm_constraint_range *uvm_md_constraints[] = {
&isa_constraint,
diff --git sys/arch/amd64/include/pci_machdep.h
sys/arch/amd64/include/pci_machdep.h
index 27b833b..bf54f31 100644
--- sys/arch/amd64/include/pci_machdep.h
+++ sys/arch/amd64/include/pci_machdep.h
@@ -41,6 +41,7 @@
*/
extern struct bus_dma_tag pci_bus_dma_tag;
+extern struct bus_dma_tag virtio_pci_bus_dma_tag;
/*
* Types provided to machine-independent PCI code
diff --git sys/arch/amd64/isa/isa_machdep.c sys/arch/amd64/isa/isa_machdep.c
index 74dc907..ec35edead 100644
--- sys/arch/amd64/isa/isa_machdep.c
+++ sys/arch/amd64/isa/isa_machdep.c
@@ -140,7 +140,7 @@ void _isa_dma_free_bouncebuf(bus_dma_tag_t,
bus_dmamap_t);
* buffers, if necessary.
*/
struct bus_dma_tag isa_bus_dma_tag = {
- NULL, /* _cookie */
+ &isa_constraint,
_isa_bus_dmamap_create,
_isa_bus_dmamap_destroy,
_isa_bus_dmamap_load,
diff --git sys/arch/amd64/pci/pci_machdep.c sys/arch/amd64/pci/pci_machdep.c
index 19983b0..5dca63a 100644
--- sys/arch/amd64/pci/pci_machdep.c
+++ sys/arch/amd64/pci/pci_machdep.c
@@ -130,7 +130,7 @@ do {
\
* of these functions.
*/
struct bus_dma_tag pci_bus_dma_tag = {
- NULL, /* _may_bounce */
+ &dma_constraint,
_bus_dmamap_create,
_bus_dmamap_destroy,
_bus_dmamap_load,
@@ -147,6 +147,25 @@ struct bus_dma_tag pci_bus_dma_tag = {
_bus_dmamem_mmap,
};
+struct bus_dma_tag virtio_pci_bus_dma_tag = {
+ &no_constraint,
+ _bus_dmamap_create,
+ _bus_dmamap_destroy,
+ _bus_dmamap_load,
+ _bus_dmamap_load_mbuf,
+ _bus_dmamap_load_uio,
+ _bus_dmamap_load_raw,
+ _bus_dmamap_unload,
+ _bus_dmamap_sync,
+ _bus_dmamem_alloc,
+ _bus_dmamem_alloc_range,
+ _bus_dmamem_free,
+ _bus_dmamem_map,
+ _bus_dmamem_unmap,
+ _bus_dmamem_mmap,
+};
+
+
void
pci_attach_hook(struct device *parent, struct device *self,
struct pcibus_attach_args *pba)
diff --git sys/arch/i386/pci/pci_machdep.h sys/arch/i386/pci/pci_machdep.h
index 2831470..6e6484b 100644
--- sys/arch/i386/pci/pci_machdep.h
+++ sys/arch/i386/pci/pci_machdep.h
@@ -56,6 +56,7 @@ union i386_pci_tag_u {
};
extern struct bus_dma_tag pci_bus_dma_tag;
+#define virtio_pci_bus_dma_tag pci_bus_dma_tag
/*
* Types provided to machine-independent PCI code
diff --git sys/dev/pci/virtio_pci.c sys/dev/pci/virtio_pci.c
index 489a449..6c08579 100644
--- sys/dev/pci/virtio_pci.c
+++ sys/dev/pci/virtio_pci.c
@@ -183,7 +183,7 @@ virtio_pci_attach(struct device *parent, struct device
*self, void *aux)
vsc->sc_ops = &virtio_pci_ops;
sc->sc_pc = pc;
- vsc->sc_dmat = pa->pa_dmat;
+ vsc->sc_dmat = &virtio_pci_bus_dma_tag;
sc->sc_config_offset = VIRTIO_CONFIG_DEVICE_CONFIG_NOMSI;
if (pci_mapreg_map(pa, PCI_MAPREG_START, PCI_MAPREG_TYPE_IO, 0,
