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Re: [PATCH v3 06/70] kvm: Introduce support for memory_attributes


From: Xiaoyao Li
Subject: Re: [PATCH v3 06/70] kvm: Introduce support for memory_attributes
Date: Thu, 21 Dec 2023 14:11:09 +0800
User-agent: Mozilla Thunderbird

On 12/12/2023 9:56 PM, Wang, Wei W wrote:
On Wednesday, November 15, 2023 3:14 PM, Xiaoyao Li wrote:
Introduce the helper functions to set the attributes of a range of memory to
private or shared.

This is necessary to notify KVM the private/shared attribute of each gpa range.
KVM needs the information to decide the GPA needs to be mapped at hva-
based shared memory or guest_memfd based private memory.

Signed-off-by: Xiaoyao Li <xiaoyao.li@intel.com>
---
  accel/kvm/kvm-all.c  | 42 ++++++++++++++++++++++++++++++++++++++++++
  include/sysemu/kvm.h |  3 +++
  2 files changed, 45 insertions(+)

diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c index
69afeb47c9c0..76e2404d54d2 100644
--- a/accel/kvm/kvm-all.c
+++ b/accel/kvm/kvm-all.c
@@ -102,6 +102,7 @@ bool kvm_has_guest_debug;  static int kvm_sstep_flags;
static bool kvm_immediate_exit;  static bool kvm_guest_memfd_supported;
+static uint64_t kvm_supported_memory_attributes;
  static hwaddr kvm_max_slot_size = ~0;

  static const KVMCapabilityInfo kvm_required_capabilites[] = { @@ -1305,6
+1306,44 @@ void kvm_set_max_memslot_size(hwaddr max_slot_size)
      kvm_max_slot_size = max_slot_size;
  }

+static int kvm_set_memory_attributes(hwaddr start, hwaddr size,
+uint64_t attr) {
+    struct kvm_memory_attributes attrs;
+    int r;
+
+    attrs.attributes = attr;
+    attrs.address = start;
+    attrs.size = size;
+    attrs.flags = 0;
+
+    r = kvm_vm_ioctl(kvm_state, KVM_SET_MEMORY_ATTRIBUTES, &attrs);
+    if (r) {
+        warn_report("%s: failed to set memory (0x%lx+%#zx) with attr 0x%lx
error '%s'",
+                     __func__, start, size, attr, strerror(errno));
+    }
+    return r;
+}
+
+int kvm_set_memory_attributes_private(hwaddr start, hwaddr size) {
+    if (!(kvm_supported_memory_attributes &
KVM_MEMORY_ATTRIBUTE_PRIVATE)) {
+        error_report("KVM doesn't support PRIVATE memory attribute\n");
+        return -EINVAL;
+    }
+
+    return kvm_set_memory_attributes(start, size,
+KVM_MEMORY_ATTRIBUTE_PRIVATE); }
+
+int kvm_set_memory_attributes_shared(hwaddr start, hwaddr size) {
+    if (!(kvm_supported_memory_attributes &
KVM_MEMORY_ATTRIBUTE_PRIVATE)) {
+        error_report("KVM doesn't support PRIVATE memory attribute\n");
+        return -EINVAL;
+    }

Duplicate code in kvm_set_memory_attributes_shared/private.
Why not move the check into kvm_set_memory_attributes?

Because it's not easy to put the check into there.

Both setting and clearing one bit require the capability check. If moving the check into kvm_set_memory_attributes(), the check of KVM_MEMORY_ATTRIBUTE_PRIVATE will have to become unconditionally, which is not aligned to the function name because the name is not restricted to shared/private attribute only.



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