On 7/15/2025 11:31 AM, Xiaoyao Li wrote:
From: Yan Zhao <yan.y.zhao@xxxxxxxxx>
(This is just the POC code to use in-place conversion gmem.)
Try to use in-place conversion gmem when it is supported.
When in-place conversion is enabled, there is no need to discard memory
since it still needs to be used as the memory of opposite attribute
after conversion.
For a upstreamable solution, we can introduce memory-backend-guestmemfd
for in-place conversion. With the non in-place conversion, it needs
seperate non-gmem memory to back the shared memory and gmem is created
implicitly and internally based on vm type. While with in-place
conversion, there is no need for seperate non-gmem memory because gmem
itself can be served as shared memory. So that we can introduce
memory-backend-guestmemfd as the specific backend for in-place
conversion gmem.
Signed-off-by: Yan Zhao <yan.y.zhao@xxxxxxxxx>
Co-developed-by Xiaoyao Li <xiaoyao.li@xxxxxxxxx>
Signed-off-by: Xiaoyao Li <xiaoyao.li@xxxxxxxxx>
---
accel/kvm/kvm-all.c | 79 ++++++++++++++++++++++++++++-----------
accel/stubs/kvm-stub.c | 1 +
include/system/kvm.h | 1 +
include/system/memory.h | 2 +
include/system/ramblock.h | 1 +
system/memory.c | 7 ++++
system/physmem.c | 21 ++++++++++-
7 files changed, 90 insertions(+), 22 deletions(-)
diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c
index a106d1ba0f0b..609537738d38 100644
--- a/accel/kvm/kvm-all.c
+++ b/accel/kvm/kvm-all.c
@@ -105,6 +105,7 @@ static int kvm_sstep_flags;
static bool kvm_immediate_exit;
static uint64_t kvm_supported_memory_attributes;
static bool kvm_guest_memfd_supported;
+bool kvm_guest_memfd_inplace_supported;
static hwaddr kvm_max_slot_size = ~0;
static const KVMCapabilityInfo kvm_required_capabilites[] = {
@@ -1487,6 +1488,30 @@ static int kvm_set_memory_attributes(hwaddr start, uint64_t size, uint64_t attr)
return r;
}
+static int kvm_set_guest_memfd_shareability(MemoryRegion *mr, ram_addr_t offset,
+ uint64_t size, bool shared)
+{
+ int guest_memfd = mr->ram_block->guest_memfd;
+ struct kvm_gmem_convert param = {
+ .offset = offset,
+ .size = size,
+ .error_offset = 0,
+ };
+ unsigned long op;
+ int r;
+
+ op = shared ? KVM_GMEM_CONVERT_SHARED : KVM_GMEM_CONVERT_PRIVATE;
+
+ r = ioctl(guest_memfd, op, ¶m);
+ if (r) {
+ error_report("failed to set guest_memfd offset 0x%lx size 0x%lx to %s "
+ "error '%s' error offset 0x%llx",
+ offset, size, shared ? "shared" : "private",
+ strerror(errno), param.error_offset);
+ }
+ return r;
+}
+
int kvm_set_memory_attributes_private(hwaddr start, uint64_t size)
{
return kvm_set_memory_attributes(start, size, KVM_MEMORY_ATTRIBUTE_PRIVATE);
@@ -1604,7 +1629,8 @@ static void kvm_set_phys_mem(KVMMemoryListener *kml,
abort();
}
- if (memory_region_has_guest_memfd(mr)) {
+ if (memory_region_has_guest_memfd(mr) &&
+ !memory_region_guest_memfd_in_place_conversion(mr)) {
err = kvm_set_memory_attributes_private(start_addr, slot_size);
if (err) {
error_report("%s: failed to set memory attribute private: %s",
@@ -2779,6 +2805,9 @@ static int kvm_init(AccelState *as, MachineState *ms)
kvm_check_extension(s, KVM_CAP_GUEST_MEMFD) &&
kvm_check_extension(s, KVM_CAP_USER_MEMORY2) &&
(kvm_supported_memory_attributes & KVM_MEMORY_ATTRIBUTE_PRIVATE);
+ kvm_guest_memfd_inplace_supported =
+ kvm_check_extension(s, KVM_CAP_GMEM_SHARED_MEM) &&
+ kvm_check_extension(s, KVM_CAP_GMEM_CONVERSION);
kvm_pre_fault_memory_supported = kvm_vm_check_extension(s, KVM_CAP_PRE_FAULT_MEMORY);
if (s->kernel_irqchip_split == ON_OFF_AUTO_AUTO) {
@@ -3056,6 +3085,7 @@ static void kvm_eat_signals(CPUState *cpu)
int kvm_convert_memory(hwaddr start, hwaddr size, bool to_private)
{
+ bool in_place_conversion = false;
MemoryRegionSection section;
ram_addr_t offset;
MemoryRegion *mr;
@@ -3112,18 +3142,23 @@ int kvm_convert_memory(hwaddr start, hwaddr size, bool to_private)
goto out_unref;
}
- if (to_private) {
- ret = kvm_set_memory_attributes_private(start, size);
- } else {
- ret = kvm_set_memory_attributes_shared(start, size);
- }
- if (ret) {
- goto out_unref;
- }
-
addr = memory_region_get_ram_ptr(mr) + section.offset_within_region;
rb = qemu_ram_block_from_host(addr, false, &offset);
+ in_place_conversion = memory_region_guest_memfd_in_place_conversion(mr);
+ if (in_place_conversion) {
+ ret = kvm_set_guest_memfd_shareability(mr, offset, size, !to_private);
+ } else {
+ if (to_private) {
+ ret = kvm_set_memory_attributes_private(start, size);
+ } else {
+ ret = kvm_set_memory_attributes_shared(start, size);
+ }
+ }
+ if (ret) {
+ goto out_unref;
+ }
+
ret = ram_block_attributes_state_change(RAM_BLOCK_ATTRIBUTES(mr->rdm),
offset, size, to_private);
if (ret) {
There's one thing required for shared device assignment with in-place conversion, we need to follow the
sequence of unmap-before-conversion-to-private and map-after-conversion-to-shared. Maybe change it like:
diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c
index a54e68e769..e9e62ae8f2 100644
--- a/accel/kvm/kvm-all.c
+++ b/accel/kvm/kvm-all.c
@@ -3146,6 +3146,17 @@ int kvm_convert_memory(hwaddr start, hwaddr size, bool to_private)
addr = memory_region_get_ram_ptr(mr) + section.offset_within_region;
rb = qemu_ram_block_from_host(addr, false, &offset);
+ if (to_private) {
+ ret = ram_block_attributes_state_change(RAM_BLOCK_ATTRIBUTES(mr->rdm),
+ offset, size, to_private);
+ if (ret) {
+ error_report("Failed to notify the listener the state change of "
+ "(0x%"HWADDR_PRIx" + 0x%"HWADDR_PRIx") to %s",
+ start, size, to_private ? "private" : "shared");
+ goto out_unref;
+ }
+ }
+
in_place_conversion = memory_region_guest_memfd_in_place_conversion(mr);
if (in_place_conversion) {
ret = kvm_set_guest_memfd_shareability(mr, offset, size, !to_private);
@@ -3160,13 +3171,15 @@ int kvm_convert_memory(hwaddr start, hwaddr size, bool to_private)
goto out_unref;
}
- ret = ram_block_attributes_state_change(RAM_BLOCK_ATTRIBUTES(mr->rdm),
- offset, size, to_private);
- if (ret) {
- error_report("Failed to notify the listener the state change of "
- "(0x%"HWADDR_PRIx" + 0x%"HWADDR_PRIx") to %s",
- start, size, to_private ? "private" : "shared");
- goto out_unref;
+ if (!to_private) {
+ ret = ram_block_attributes_state_change(RAM_BLOCK_ATTRIBUTES(mr->rdm),
+ offset, size, to_private);
+ if (ret) {
+ error_report("Failed to notify the listener the state change of "
+ "(0x%"HWADDR_PRIx" + 0x%"HWADDR_PRIx") to %s",
+ start, size, to_private ? "private" : "shared");
+ goto out_unref;
+ }
}
