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;
+ }
}
