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

[Xiaoyao Li <xiaoyao.li@intel.com>]

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.