Re: [PATCH v3 05/70] kvm: Enable KVM_SET_USER_MEMORY_REGION2 for memslot

[Isaku Yamahata]

On Wed, Nov 15, 2023 at 02:14:14AM -0500,
Xiaoyao Li <xiaoyao.li@intel.com> wrote:

> From: Chao Peng <chao.p.peng@linux.intel.com>
> 
> Switch to KVM_SET_USER_MEMORY_REGION2 when supported by KVM.
> 
> With KVM_SET_USER_MEMORY_REGION2, QEMU can set up memory region that
> backend'ed both by hva-based shared memory and guest memfd based private
> memory.
> 
> Signed-off-by: Chao Peng <chao.p.peng@linux.intel.com>
> Co-developed-by: Xiaoyao Li <xiaoyao.li@intel.com>
> Signed-off-by: Xiaoyao Li <xiaoyao.li@intel.com>
> ---
>  accel/kvm/kvm-all.c      | 56 ++++++++++++++++++++++++++++++++++------
>  accel/kvm/trace-events   |  2 +-
>  include/sysemu/kvm_int.h |  2 ++
>  3 files changed, 51 insertions(+), 9 deletions(-)
> 
> diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c
> index 9f751d4971f8..69afeb47c9c0 100644
> --- a/accel/kvm/kvm-all.c
> +++ b/accel/kvm/kvm-all.c
> @@ -293,35 +293,69 @@ int kvm_physical_memory_addr_from_host(KVMState *s, 
> void *ram,
>  static int kvm_set_user_memory_region(KVMMemoryListener *kml, KVMSlot *slot, 
> bool new)
>  {
>      KVMState *s = kvm_state;
> -    struct kvm_userspace_memory_region mem;
> +    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;
>      mem.flags = slot->flags;
> +    mem.guest_memfd = slot->guest_memfd;
> +    mem.guest_memfd_offset = slot->guest_memfd_offset;
>  
>      if (slot->memory_size && !new && (mem.flags ^ slot->old_flags) & 
> KVM_MEM_READONLY) {
>          /* Set the slot size to 0 before setting the slot to the desired
>           * value. This is needed based on KVM commit 75d61fbc. */
>          mem.memory_size = 0;
> -        ret = kvm_vm_ioctl(s, KVM_SET_USER_MEMORY_REGION, &mem);
> +
> +        if (cap_user_memory2) {
> +            ret = kvm_vm_ioctl(s, KVM_SET_USER_MEMORY_REGION2, &mem);
> +        } else {
> +            ret = kvm_vm_ioctl(s, KVM_SET_USER_MEMORY_REGION, &mem);
> +         }
>          if (ret < 0) {
>              goto err;
>          }
>      }
>      mem.memory_size = slot->memory_size;
> -    ret = kvm_vm_ioctl(s, KVM_SET_USER_MEMORY_REGION, &mem);
> +    if (cap_user_memory2) {
> +        ret = kvm_vm_ioctl(s, KVM_SET_USER_MEMORY_REGION2, &mem);
> +    } else {
> +        ret = kvm_vm_ioctl(s, KVM_SET_USER_MEMORY_REGION, &mem);
> +    }
>      slot->old_flags = mem.flags;
>  err:
>      trace_kvm_set_user_memory(mem.slot >> 16, (uint16_t)mem.slot, mem.flags,
>                                mem.guest_phys_addr, mem.memory_size,
> -                              mem.userspace_addr, ret);
> +                              mem.userspace_addr, mem.guest_memfd,
> +                              mem.guest_memfd_offset, ret);
>      if (ret < 0) {
> -        error_report("%s: KVM_SET_USER_MEMORY_REGION failed, slot=%d,"
> -                     " start=0x%" PRIx64 ", size=0x%" PRIx64 ": %s",
> -                     __func__, mem.slot, slot->start_addr,
> -                     (uint64_t)mem.memory_size, strerror(errno));
> +        if (cap_user_memory2) {
> +                error_report("%s: KVM_SET_USER_MEMORY_REGION2 failed, 
> slot=%d,"
> +                        " start=0x%" PRIx64 ", size=0x%" PRIx64 ","
> +                        " flags=0x%" PRIx32 ", guest_memfd=%" PRId32 ","
> +                        " guest_memfd_offset=0x%" PRIx64 ": %s",
> +                        __func__, mem.slot, slot->start_addr,
> +                        (uint64_t)mem.memory_size, mem.flags,
> +                        mem.guest_memfd, (uint64_t)mem.guest_memfd_offset,
> +                        strerror(errno));
> +        } else {
> +                error_report("%s: KVM_SET_USER_MEMORY_REGION failed, 
> slot=%d,"
> +                            " start=0x%" PRIx64 ", size=0x%" PRIx64 ": %s",
> +                            __func__, mem.slot, slot->start_addr,
> +                            (uint64_t)mem.memory_size, strerror(errno));
> +        }
>      }
>      return ret;
>  }
> @@ -477,6 +511,9 @@ static int kvm_mem_flags(MemoryRegion *mr)
>      if (readonly && kvm_readonly_mem_allowed) {
>          flags |= KVM_MEM_READONLY;
>      }
> +    if (memory_region_has_guest_memfd(mr)) {
> +        flags |= KVM_MEM_PRIVATE;
> +    }

Nitpick: it was renamed to KVM_MEM_GUEST_MEMFD
As long as the value is defined to same value, it doesn't matter, though.
-- 
Isaku Yamahata <isaku.yamahata@linux.intel.com>