Ben-Ami Yassour wrote:
Amit,
Below is the patch for PCI passthrough tree, it enables a guest to
access a device's
memory mapped I/O regions directly, without requiring the host to trap
and
emulate every MMIO access.
This patch requires only userspace changes and it is relaying on the
kernel patch by Anthony: "Handle vma regions with no backing page".
Note that this patch requires CONFIG_NUMA to be set. It does require a
change to the VT-d that Allen sent a while ago, to avoid mapping of
memory slots with no backing page.
diff --git a/libkvm/libkvm.c b/libkvm/libkvm.c
index d1e95a4..ce062cb 100644
--- a/libkvm/libkvm.c
+++ b/libkvm/libkvm.c
@@ -400,7 +400,7 @@ void *kvm_create_userspace_phys_mem(kvm_context_t
kvm, unsigned long phys_start,
{
int r;
int prot = PROT_READ;
- void *ptr;
+ void *ptr = NULL;
struct kvm_userspace_memory_region memory = {
.memory_size = len,
.guest_phys_addr = phys_start,
@@ -410,16 +410,24 @@ void
*kvm_create_userspace_phys_mem(kvm_context_t kvm, unsigned long
phys_start,
if (writable)
prot |= PROT_WRITE;
- ptr = mmap(NULL, len, prot, MAP_ANONYMOUS | MAP_SHARED, -1, 0);
- if (ptr == MAP_FAILED) {
- fprintf(stderr, "create_userspace_phys_mem: %s",
strerror(errno));
- return 0;
- }
+ if (len > 0) {
+ ptr = mmap(NULL, len, prot, MAP_ANONYMOUS | MAP_SHARED, -1, 0);
+ if (ptr == MAP_FAILED) {
+ fprintf(stderr, "create_userspace_phys_mem: %s",
+ strerror(errno));
+ return 0;
+ }
You're using 'len == 0' here to change the semantics of the function.
It would be better to have two different APIs (perhaps sharing some of
the implementation by calling a helper).
--
Do not meddle in the internals of kernels, for they are subtle and quick to
panic.
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