Re: [PATCH v3 10/70] kvm: handle KVM_EXIT_MEMORY_FAULT

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On 11/15/2023 6:42 PM, Daniel P. Berrangé wrote:
On Wed, Nov 15, 2023 at 02:14:19AM -0500, Xiaoyao Li wrote:
From: Chao Peng <chao.p.peng@xxxxxxxxxxxxxxx>

Currently only KVM_MEMORY_EXIT_FLAG_PRIVATE in flags is valid when
KVM_EXIT_MEMORY_FAULT happens. It indicates userspace needs to do
the memory conversion on the RAMBlock to turn the memory into desired
attribute, i.e., private/shared.

Note, KVM_EXIT_MEMORY_FAULT makes sense only when the RAMBlock has
guest_memfd memory backend.

Note, KVM_EXIT_MEMORY_FAULT returns with -EFAULT, so special handling is
added.

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 | 76 +++++++++++++++++++++++++++++++++++++++------
  1 file changed, 66 insertions(+), 10 deletions(-)

diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c
index 76e2404d54d2..58abbcb6926e 100644
--- a/accel/kvm/kvm-all.c
+++ b/accel/kvm/kvm-all.c
@@ -2902,6 +2902,50 @@ static void kvm_eat_signals(CPUState *cpu)
      } while (sigismember(&chkset, SIG_IPI));
  }
+static int kvm_convert_memory(hwaddr start, hwaddr size, bool to_private)
+{
+    MemoryRegionSection section;
+    ram_addr_t offset;
+    RAMBlock *rb;
+    void *addr;
+    int ret = -1;
+
+    section = memory_region_find(get_system_memory(), start, size);
+    if (!section.mr) {
+        return ret;
+    }
+
+    if (memory_region_has_guest_memfd(section.mr)) {
+        if (to_private) {
+            ret = kvm_set_memory_attributes_private(start, size);
+        } else {
+            ret = kvm_set_memory_attributes_shared(start, size);
+        }
+
+        if (ret) {
+            memory_region_unref(section.mr);
+            return ret;
+        }
+
+        addr = memory_region_get_ram_ptr(section.mr) +
+               section.offset_within_region;
+        rb = qemu_ram_block_from_host(addr, false, &offset);
+        /*
+         * With KVM_SET_MEMORY_ATTRIBUTES by kvm_set_memory_attributes(),
+         * operation on underlying file descriptor is only for releasing
+         * unnecessary pages.
+         */
+        ram_block_convert_range(rb, offset, size, to_private);
+    } else {
+        warn_report("Convert non guest_memfd backed memory region "
+                    "(0x%"HWADDR_PRIx" ,+ 0x%"HWADDR_PRIx") to %s",
+                    start, size, to_private ? "private" : "shared");

Again, if you're returning '-1' to indicate error, then
using warn_report is wrong, it should be error_report.

warn_report is for when you return success, indicating
the problem was non-fatal.

Learned.

Thanks!

+    }
+
+    memory_region_unref(section.mr);
+    return ret;
+}
+
  int kvm_cpu_exec(CPUState *cpu)
  {
      struct kvm_run *run = cpu->kvm_run;
@@ -2969,18 +3013,20 @@ int kvm_cpu_exec(CPUState *cpu)
                  ret = EXCP_INTERRUPT;
                  break;
              }
-            fprintf(stderr, "error: kvm run failed %s\n",
-                    strerror(-run_ret));
+            if (!(run_ret == -EFAULT && run->exit_reason == KVM_EXIT_MEMORY_FAULT)) {
+                fprintf(stderr, "error: kvm run failed %s\n",
+                        strerror(-run_ret));
  #ifdef TARGET_PPC
-            if (run_ret == -EBUSY) {
-                fprintf(stderr,
-                        "This is probably because your SMT is enabled.\n"
-                        "VCPU can only run on primary threads with all "
-                        "secondary threads offline.\n");
-            }
+                if (run_ret == -EBUSY) {
+                    fprintf(stderr,
+                            "This is probably because your SMT is enabled.\n"
+                            "VCPU can only run on primary threads with all "
+                            "secondary threads offline.\n");
+                }
  #endif
-            ret = -1;
-            break;
+                ret = -1;
+                break;
+            }
          }
trace_kvm_run_exit(cpu->cpu_index, run->exit_reason);
@@ -3067,6 +3113,16 @@ int kvm_cpu_exec(CPUState *cpu)
                  break;
              }
              break;
+        case KVM_EXIT_MEMORY_FAULT:
+            if (run->memory_fault.flags & ~KVM_MEMORY_EXIT_FLAG_PRIVATE) {
+                error_report("KVM_EXIT_MEMORY_FAULT: Unknown flag 0x%" PRIx64,
+                             (uint64_t)run->memory_fault.flags);
+                ret = -1;
+                break;
+            }
+            ret = kvm_convert_memory(run->memory_fault.gpa, run->memory_fault.size,
+                                     run->memory_fault.flags & KVM_MEMORY_EXIT_FLAG_PRIVATE);
+            break;
          default:
              DPRINTF("kvm_arch_handle_exit\n");
              ret = kvm_arch_handle_exit(cpu, run);
--
2.34.1


With regards,
Daniel





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