Re: [RFC PATCH 15/19] kvm: handle KVM_EXIT_MEMORY_FAULT

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

On 8/9/2023 11:02 PM, Xu Yilun wrote:
> On 2023-07-31 at 12:21:57 -0400, Xiaoyao Li wrote:
>> From: Chao Peng <chao.p.peng@linux.intel.com>
>>
>> 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
>> gmem memory backend.
>>
>> Signed-off-by: Chao Peng <chao.p.peng@linux.intel.com>
>> Signed-off-by: Xiaoyao Li <xiaoyao.li@intel.com>
>> ---
>>   accel/kvm/kvm-all.c | 52 +++++++++++++++++++++++++++++++++++++++++++++
>>   1 file changed, 52 insertions(+)
>>
>> diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c
>> index f9b5050b8885..72d50b923bf2 100644
>> --- a/accel/kvm/kvm-all.c
>> +++ b/accel/kvm/kvm-all.c
>> @@ -3040,6 +3040,48 @@ 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;
>> +    void *addr;
>> +    RAMBlock *rb;
>> +    ram_addr_t offset;
>> +    int ret = -1;
>> +
>> +    section = memory_region_find(get_system_memory(), start, size);
>> +    if (!section.mr) {
>> +        return ret;
>> +    }
>> +
>> +    if (memory_region_can_be_private(section.mr)) {
>> +        if (to_private) {
>> +            ret = kvm_set_memory_attributes_private(start, size);
>> +        } else {
>> +            ret = kvm_set_memory_attributes_shared(start, size);
>> +        }
>> +
>> +        if (ret) {
>> +            return ret;
> 
> Should we unref the memory region before return?

Thanks for catching this!

> Thanks,
> Yilun
> 
>> +        }
>> +
>> +        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");
>> +    }
>> +
>> +    memory_region_unref(section.mr);
>> +    return ret;
>> +}