On 10/14/25 5:02 AM, Michael S. Tsirkin wrote:
On Tue, Oct 14, 2025 at 11:13:51AM +0530, Sairaj Kodilkar wrote:
On 10/13/2025 1:45 PM, Michael S. Tsirkin wrote:
On Mon, Oct 13, 2025 at 10:30:45AM +0530, Sairaj Kodilkar wrote:
The AMD IOMMU is set up at boot time and uses PCI bus numbers + devfn
for indexing into DTE. The problem is that before the guest started,
all PCI bus numbers are 0 as no PCI discovery happened yet (BIOS or/and
kernel will do that later) so relying on the bus number is wrong.
The immediate effect is emulated devices cannot do DMA when places on
a bus other that 0.
Replace static array of address_space with hash table which uses devfn and
PCIBus* for key as it is not going to change after the guest is booted.
I am curious whether this has any measureable impact on
performance.
I dont think it should have much performance impact, as guest usually has
small number of devices attached to it and hash has O(1) average search cost
when hash key function is good.
Co-developed-by: Alexey Kardashevskiy <[email protected]>
Signed-off-by: Alexey Kardashevskiy <[email protected]>
Signed-off-by: Sairaj Kodilkar <[email protected]>
love the patch! yet something to improve:
---
hw/i386/amd_iommu.c | 134 ++++++++++++++++++++++++++------------------
hw/i386/amd_iommu.h | 2 +-
2 files changed, 79 insertions(+), 57 deletions(-)
diff --git a/hw/i386/amd_iommu.c b/hw/i386/amd_iommu.c
index 378e0cb55eab..b194e3294dd7 100644
--- a/hw/i386/amd_iommu.c
+++ b/hw/i386/amd_iommu.c
@@ -59,7 +59,7 @@ const char *amdvi_mmio_high[] = {
};
struct AMDVIAddressSpace {
- uint8_t bus_num; /* bus number */
+ PCIBus *bus; /* PCIBus (for bus number) */
uint8_t devfn; /* device function */
AMDVIState *iommu_state; /* AMDVI - one per machine */
MemoryRegion root; /* AMDVI Root memory map region */
@@ -101,6 +101,11 @@ typedef enum AMDVIFaultReason {
AMDVI_FR_PT_ENTRY_INV, /* Failure to read PTE from guest memory */
} AMDVIFaultReason;
+typedef struct amdvi_as_key {
+ PCIBus *bus;
+ uint8_t devfn;
+} amdvi_as_key;
+
uint64_t amdvi_extended_feature_register(AMDVIState *s)
{
uint64_t feature = AMDVI_DEFAULT_EXT_FEATURES;
Pls fix structure and typedef names according to the QEMU
coding style. Thanks!
This is something I am struggling with, because the name
`AMDVIASKey` does not offer readability.
AMDVIAsKey
Or you can update all code to use AmdVi and get AmdViAsKey if you prefer.
Maybe we can come
up with an alternate style which is readable and does not
differ much from the current style.
@alejandro any suggestions ?
I should have pointed out the CamelCase requirement for the typedef on
v1. My initial reaction was: "do not use typedef" and go with the
slightly longer 'struct amdvi_as_key' instead. The style guide has a
warning about typedefs (which doesn't necessarily apply here), but IMO
still better to avoid it in this case were we are not really gaining
much from it.
If I were to use a typedef I would use 'AMDViAsKey'. After all, the 'i'
in AMD-Vi and 'd' in VT-d are lowercase ;)
But my opinion is to avoid the typedef altogether.
@@ -382,6 +387,44 @@ static guint amdvi_uint64_hash(gconstpointer v)
return (guint)*(const uint64_t *)v;
}
+static gboolean amdvi_as_equal(gconstpointer v1, gconstpointer v2)
+{
+ const struct amdvi_as_key *key1 = v1;
+ const struct amdvi_as_key *key2 = v2;
+
+ return key1->bus == key2->bus && key1->devfn == key2->devfn;
+}
+
+static guint amdvi_as_hash(gconstpointer v)
+{
+ const struct amdvi_as_key *key = v;
+ guint bus = (guint)(uintptr_t)key->bus;
+
+ return (guint)(bus << 8 | (uint)key->devfn);
+}
+
+static AMDVIAddressSpace *amdvi_as_lookup(AMDVIState *s, PCIBus *bus,
+ uint8_t devfn)
+{
+ amdvi_as_key key = { .bus = bus, .devfn = devfn };
+ return g_hash_table_lookup(s->address_spaces, &key);
+}
+
+gboolean amdvi_find_as_by_devid(gpointer key, gpointer value,
+ gpointer user_data)
+{
+ amdvi_as_key *as = (struct amdvi_as_key *)key;
this assignment does not need a cast I think.
Agree. And assuming you take my advice of not using a typedef, the line
should be:
const struct amdvi_as_key *as = key;
to follow the style guide directive of using "const-correct" pointers.
Putting back the static qualifier from my earlier reply:
static gboolean amdvi_find_as_by_devid(gpointer key, gpointer value,
gpointer user_data)
{
const struct amdvi_as_key *as = key;
const uint16_t *devidp = user_data;
return *devidp == PCI_BUILD_BDF(pci_bus_num(as->bus), as->devfn);
}
Thank you,
Alejandro
+ uint16_t devid = *((uint16_t *)user_data);
would be better like this:
uint16_t * devidp = user_data;
then just use *devidp instead of devid.
sure
Thanks
Sairaj
