Re: [PATCH v3 05/70] kvm: Enable KVM_SET_USER_MEMORY_REGION2 for memslot

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On 11/18/2023 4:50 AM, Isaku Yamahata wrote:
On Wed, Nov 15, 2023 at 02:14:14AM -0500,
Xiaoyao Li <xiaoyao.li@xxxxxxxxx> wrote:

From: Chao Peng <chao.p.peng@xxxxxxxxxxxxxxx>

Switch to KVM_SET_USER_MEMORY_REGION2 when supported by KVM.

With KVM_SET_USER_MEMORY_REGION2, QEMU can set up memory region that
backend'ed both by hva-based shared memory and guest memfd based private
memory.

Signed-off-by: Chao Peng <chao.p.peng@xxxxxxxxxxxxxxx>
Co-developed-by: Xiaoyao Li <xiaoyao.li@xxxxxxxxx>
Signed-off-by: Xiaoyao Li <xiaoyao.li@xxxxxxxxx>
---
  accel/kvm/kvm-all.c      | 56 ++++++++++++++++++++++++++++++++++------
  accel/kvm/trace-events   |  2 +-
  include/sysemu/kvm_int.h |  2 ++
  3 files changed, 51 insertions(+), 9 deletions(-)

diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c
index 9f751d4971f8..69afeb47c9c0 100644
--- a/accel/kvm/kvm-all.c
+++ b/accel/kvm/kvm-all.c
@@ -293,35 +293,69 @@ int kvm_physical_memory_addr_from_host(KVMState *s, void *ram,
  static int kvm_set_user_memory_region(KVMMemoryListener *kml, KVMSlot *slot, bool new)
  {
      KVMState *s = kvm_state;
-    struct kvm_userspace_memory_region mem;
+    struct kvm_userspace_memory_region2 mem;
+    static int cap_user_memory2 = -1;
      int ret;
+ if (cap_user_memory2 == -1) {
+        cap_user_memory2 = kvm_check_extension(s, KVM_CAP_USER_MEMORY2);
+    }
+
+    if (!cap_user_memory2 && slot->guest_memfd >= 0) {
+        error_report("%s, KVM doesn't support KVM_CAP_USER_MEMORY2,"
+                     " which is required by guest memfd!", __func__);
+        exit(1);
+    }
+
      mem.slot = slot->slot | (kml->as_id << 16);
      mem.guest_phys_addr = slot->start_addr;
      mem.userspace_addr = (unsigned long)slot->ram;
      mem.flags = slot->flags;
+    mem.guest_memfd = slot->guest_memfd;
+    mem.guest_memfd_offset = slot->guest_memfd_offset;
if (slot->memory_size && !new && (mem.flags ^ slot->old_flags) & KVM_MEM_READONLY) {
          /* Set the slot size to 0 before setting the slot to the desired
           * value. This is needed based on KVM commit 75d61fbc. */
          mem.memory_size = 0;
-        ret = kvm_vm_ioctl(s, KVM_SET_USER_MEMORY_REGION, &mem);
+
+        if (cap_user_memory2) {
+            ret = kvm_vm_ioctl(s, KVM_SET_USER_MEMORY_REGION2, &mem);
+        } else {
+            ret = kvm_vm_ioctl(s, KVM_SET_USER_MEMORY_REGION, &mem);
+	    }
          if (ret < 0) {
              goto err;
          }
      }
      mem.memory_size = slot->memory_size;
-    ret = kvm_vm_ioctl(s, KVM_SET_USER_MEMORY_REGION, &mem);
+    if (cap_user_memory2) {
+        ret = kvm_vm_ioctl(s, KVM_SET_USER_MEMORY_REGION2, &mem);
+    } else {
+        ret = kvm_vm_ioctl(s, KVM_SET_USER_MEMORY_REGION, &mem);
+    }
      slot->old_flags = mem.flags;
  err:
      trace_kvm_set_user_memory(mem.slot >> 16, (uint16_t)mem.slot, mem.flags,
                                mem.guest_phys_addr, mem.memory_size,
-                              mem.userspace_addr, ret);
+                              mem.userspace_addr, mem.guest_memfd,
+                              mem.guest_memfd_offset, ret);
      if (ret < 0) {
-        error_report("%s: KVM_SET_USER_MEMORY_REGION failed, slot=%d,"
-                     " start=0x%" PRIx64 ", size=0x%" PRIx64 ": %s",
-                     __func__, mem.slot, slot->start_addr,
-                     (uint64_t)mem.memory_size, strerror(errno));
+        if (cap_user_memory2) {
+                error_report("%s: KVM_SET_USER_MEMORY_REGION2 failed, slot=%d,"
+                        " start=0x%" PRIx64 ", size=0x%" PRIx64 ","
+                        " flags=0x%" PRIx32 ", guest_memfd=%" PRId32 ","
+                        " guest_memfd_offset=0x%" PRIx64 ": %s",
+                        __func__, mem.slot, slot->start_addr,
+                        (uint64_t)mem.memory_size, mem.flags,
+                        mem.guest_memfd, (uint64_t)mem.guest_memfd_offset,
+                        strerror(errno));
+        } else {
+                error_report("%s: KVM_SET_USER_MEMORY_REGION failed, slot=%d,"
+                            " start=0x%" PRIx64 ", size=0x%" PRIx64 ": %s",
+                            __func__, mem.slot, slot->start_addr,
+                            (uint64_t)mem.memory_size, strerror(errno));
+        }
      }
      return ret;
  }
@@ -477,6 +511,9 @@ static int kvm_mem_flags(MemoryRegion *mr)
      if (readonly && kvm_readonly_mem_allowed) {
          flags |= KVM_MEM_READONLY;
      }
+    if (memory_region_has_guest_memfd(mr)) {
+        flags |= KVM_MEM_PRIVATE;
+    }

Nitpick: it was renamed to KVM_MEM_GUEST_MEMFD
As long as the value is defined to same value, it doesn't matter, though.

thanks for the reminder!

Will update the headers and switch to KVM_MEM_GUEST_MEMFD.




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