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Re: [PATCH v3 09/49] kvm: Enable KVM_SET_USER_MEMORY_REGION2 for memslot
From: |
Paolo Bonzini |
Subject: |
Re: [PATCH v3 09/49] kvm: Enable KVM_SET_USER_MEMORY_REGION2 for memslot |
Date: |
Wed, 20 Mar 2024 16:56:40 +0100 |
User-agent: |
Mozilla Thunderbird |
On 3/20/24 09:39, Michael Roth wrote:
+ 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);
+ }
It's easier and more robust (for error reporting purposes) to check both
KVM_CAP_GUEST_MEMFD and KVM_CAP_USER_MEMORY2 at once in the earlier
patches:
- kvm_guest_memfd_supported = kvm_check_extension(s, KVM_CAP_GUEST_MEMFD);
+ kvm_guest_memfd_supported =
+ kvm_check_extension(s, KVM_CAP_GUEST_MEMFD) &&
+ kvm_check_extension(s, KVM_CAP_USER_MEMORY2);
since KVM cannot really support guest_memfd if it cannot then use it
to create private memory slots.
And then, this one can be changed to also use kvm_guest_memfd_supported:
diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c
index e83429b31eb..afcf6f87045 100644
--- a/accel/kvm/kvm-all.c
+++ b/accel/kvm/kvm-all.c
@@ -284,19 +284,8 @@ static int kvm_set_user_memory_region(KVMMemoryListener
*kml, KVMSlot *slot, boo
{
KVMState *s = kvm_state;
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;
@@ -309,7 +298,7 @@ static int kvm_set_user_memory_region(KVMMemoryListener
*kml, KVMSlot *slot, boo
* value. This is needed based on KVM commit 75d61fbc. */
mem.memory_size = 0;
- if (cap_user_memory2) {
+ if (kvm_guest_memfd_supported) {
ret = kvm_vm_ioctl(s, KVM_SET_USER_MEMORY_REGION2, &mem);
} else {
ret = kvm_vm_ioctl(s, KVM_SET_USER_MEMORY_REGION, &mem);
@@ -319,7 +308,7 @@ static int kvm_set_user_memory_region(KVMMemoryListener
*kml, KVMSlot *slot, boo
}
}
mem.memory_size = slot->memory_size;
- if (cap_user_memory2) {
+ if (kvm_guest_memfd_supported) {
ret = kvm_vm_ioctl(s, KVM_SET_USER_MEMORY_REGION2, &mem);
} else {
ret = kvm_vm_ioctl(s, KVM_SET_USER_MEMORY_REGION, &mem);
@@ -331,7 +320,7 @@ err:
mem.userspace_addr, mem.guest_memfd,
mem.guest_memfd_offset, ret);
if (ret < 0) {
- if (cap_user_memory2) {
+ if (kvm_guest_memfd_supported) {
error_report("%s: KVM_SET_USER_MEMORY_REGION2 failed, slot=%d,"
" start=0x%" PRIx64 ", size=0x%" PRIx64 ","
" flags=0x%" PRIx32 ", guest_memfd=%" PRId32 ","
@@ -501,6 +490,7 @@ static int kvm_mem_flags(MemoryRegion *mr)
flags |= KVM_MEM_READONLY;
}
if (memory_region_has_guest_memfd(mr)) {
+ assert(kvm_guest_memfd_supported);
flags |= KVM_MEM_GUEST_MEMFD;
}
return flags;
[PATCH v3 12/49] kvm: handle KVM_EXIT_MEMORY_FAULT, Michael Roth, 2024/03/20