Re: [Qemu-devel] [PATCH for-4.2 v3 1/2] kvm: s390: split too big memory section on several memslots

[Christian Borntraeger <borntraeger@de.ibm.com>]

On 02.08.19 15:32, Igor Mammedov wrote:
> Max memslot size supported by kvm on s390 is 8Tb,
> move logic of splitting RAM in chunks upto 8T to KVM code.
> 
> This way it will hide KVM specific restrictions in KVM code
> and won't affect baord level design decisions. Which would allow
> us to avoid misusing memory_region_allocate_system_memory() API
> and eventually use a single hostmem backend for guest RAM.
> 
> Signed-off-by: Igor Mammedov <imammedo@redhat.com>
> ---
> patch prepares only KVM side for switching to single RAM memory region
> another patch will take care of  dropping manual RAM partitioning in
> s390 code.
> ---


/home/cborntra/REPOS/qemu/target/s390x/kvm.c: In function ‘kvm_arch_init’:
/home/cborntra/REPOS/qemu/target/s390x/kvm.c:350:5: error: implicit declaration of function ‘kvm_set_max_memslot_size’; did you mean ‘kvm_get_max_memslots’? [-Werror=implicit-function-declaration]
  350 |     kvm_set_max_memslot_size(KVM_SLOT_MAX_BYTES);
      |     ^~~~~~~~~~~~~~~~~~~~~~~~
      |     kvm_get_max_memslots
/home/cborntra/REPOS/qemu/target/s390x/kvm.c:350:5: error: nested extern declaration of ‘kvm_set_max_memslot_size’ [-Werror=nested-externs]
cc1: all warnings being treated as errors
make[1]: *** [/home/cborntra/REPOS/qemu/rules.mak:69: target/s390x/kvm.o] Error 1
make: *** [Makefile:472: s390x-softmmu/all] Error 2


We probably need an include of sysemu/kvm_int.h in target/s390x/kvm.c
I will test with that fixup....

>  include/hw/s390x/s390-virtio-ccw.h | 10 ++++
>  include/sysemu/kvm_int.h           |  1 +
>  accel/kvm/kvm-all.c                | 79 ++++++++++++++++++------------
>  hw/s390x/s390-virtio-ccw.c         |  9 ----
>  target/s390x/kvm.c                 |  1 +
>  5 files changed, 60 insertions(+), 40 deletions(-)
> 
> diff --git a/include/hw/s390x/s390-virtio-ccw.h b/include/hw/s390x/s390-virtio-ccw.h
> index 8aa27199c9..00632f94b4 100644
> --- a/include/hw/s390x/s390-virtio-ccw.h
> +++ b/include/hw/s390x/s390-virtio-ccw.h
> @@ -21,6 +21,16 @@
>  #define S390_MACHINE_CLASS(klass) \
>      OBJECT_CLASS_CHECK(S390CcwMachineClass, (klass), TYPE_S390_CCW_MACHINE)
>  
> +/*
> + * KVM does only support memory slots up to KVM_MEM_MAX_NR_PAGES pages
> + * as the dirty bitmap must be managed by bitops that take an int as
> + * position indicator. If we have a guest beyond that we will split off
> + * new subregions. The split must happen on a segment boundary (1MB).
> + */
> +#define KVM_MEM_MAX_NR_PAGES ((1ULL << 31) - 1)
> +#define SEG_MSK (~0xfffffULL)
> +#define KVM_SLOT_MAX_BYTES ((KVM_MEM_MAX_NR_PAGES * TARGET_PAGE_SIZE) & SEG_MSK)
> +
>  typedef struct S390CcwMachineState {
>      /*< private >*/
>      MachineState parent_obj;
> diff --git a/include/sysemu/kvm_int.h b/include/sysemu/kvm_int.h
> index 31df465fdc..7f7520bce2 100644
> --- a/include/sysemu/kvm_int.h
> +++ b/include/sysemu/kvm_int.h
> @@ -41,4 +41,5 @@ typedef struct KVMMemoryListener {
>  void kvm_memory_listener_register(KVMState *s, KVMMemoryListener *kml,
>                                    AddressSpace *as, int as_id);
>  
> +void kvm_set_max_memslot_size(hwaddr max_slot_size);
>  #endif
> diff --git a/accel/kvm/kvm-all.c b/accel/kvm/kvm-all.c
> index f450f25295..7a6efb9612 100644
> --- a/accel/kvm/kvm-all.c
> +++ b/accel/kvm/kvm-all.c
> @@ -138,6 +138,7 @@ bool kvm_direct_msi_allowed;
>  bool kvm_ioeventfd_any_length_allowed;
>  bool kvm_msi_use_devid;
>  static bool kvm_immediate_exit;
> +static hwaddr kvm_max_slot_size = ~0;
>  
>  static const KVMCapabilityInfo kvm_required_capabilites[] = {
>      KVM_CAP_INFO(USER_MEMORY),
> @@ -951,6 +952,14 @@ kvm_check_extension_list(KVMState *s, const KVMCapabilityInfo *list)
>      return NULL;
>  }
>  
> +void kvm_set_max_memslot_size(hwaddr max_slot_size)
> +{
> +    g_assert(
> +        ROUND_UP(max_slot_size, qemu_real_host_page_size) == max_slot_size
> +    );
> +    kvm_max_slot_size = max_slot_size;
> +}
> +
>  static void kvm_set_phys_mem(KVMMemoryListener *kml,
>                               MemoryRegionSection *section, bool add)
>  {
> @@ -958,7 +967,7 @@ static void kvm_set_phys_mem(KVMMemoryListener *kml,
>      int err;
>      MemoryRegion *mr = section->mr;
>      bool writeable = !mr->readonly && !mr->rom_device;
> -    hwaddr start_addr, size;
> +    hwaddr start_addr, size, slot_size;
>      void *ram;
>  
>      if (!memory_region_is_ram(mr)) {
> @@ -983,41 +992,49 @@ static void kvm_set_phys_mem(KVMMemoryListener *kml,
>      kvm_slots_lock(kml);
>  
>      if (!add) {
> -        mem = kvm_lookup_matching_slot(kml, start_addr, size);
> -        if (!mem) {
> -            goto out;
> -        }
> -        if (mem->flags & KVM_MEM_LOG_DIRTY_PAGES) {
> -            kvm_physical_sync_dirty_bitmap(kml, section);
> -        }
> +        do {
> +            slot_size = kvm_max_slot_size < size ? kvm_max_slot_size : size;
> +            mem = kvm_lookup_matching_slot(kml, start_addr, slot_size);
> +            if (!mem) {
> +                goto out;
> +            }
> +            if (mem->flags & KVM_MEM_LOG_DIRTY_PAGES) {
> +                kvm_physical_sync_dirty_bitmap(kml, section);
> +            }
>  
> -        /* unregister the slot */
> -        g_free(mem->dirty_bmap);
> -        mem->dirty_bmap = NULL;
> -        mem->memory_size = 0;
> -        mem->flags = 0;
> -        err = kvm_set_user_memory_region(kml, mem, false);
> -        if (err) {
> -            fprintf(stderr, "%s: error unregistering slot: %s\n",
> -                    __func__, strerror(-err));
> -            abort();
> -        }
> +            /* unregister the slot */
> +            g_free(mem->dirty_bmap);
> +            mem->dirty_bmap = NULL;
> +            mem->memory_size = 0;
> +            mem->flags = 0;
> +            err = kvm_set_user_memory_region(kml, mem, false);
> +            if (err) {
> +                fprintf(stderr, "%s: error unregistering slot: %s\n",
> +                        __func__, strerror(-err));
> +                abort();
> +            }
> +            start_addr += slot_size;
> +        } while ((size -= slot_size));
>          goto out;
>      }
>  
>      /* register the new slot */
> -    mem = kvm_alloc_slot(kml);
> -    mem->memory_size = size;
> -    mem->start_addr = start_addr;
> -    mem->ram = ram;
> -    mem->flags = kvm_mem_flags(mr);
> -
> -    err = kvm_set_user_memory_region(kml, mem, true);
> -    if (err) {
> -        fprintf(stderr, "%s: error registering slot: %s\n", __func__,
> -                strerror(-err));
> -        abort();
> -    }
> +    do {
> +        slot_size = kvm_max_slot_size < size ? kvm_max_slot_size : size;
> +        mem = kvm_alloc_slot(kml);
> +        mem->memory_size = slot_size;
> +        mem->start_addr = start_addr;
> +        mem->ram = ram;
> +        mem->flags = kvm_mem_flags(mr);
> +
> +        err = kvm_set_user_memory_region(kml, mem, true);
> +        if (err) {
> +            fprintf(stderr, "%s: error registering slot: %s\n", __func__,
> +                    strerror(-err));
> +            abort();
> +        }
> +        start_addr += slot_size;
> +    } while ((size -= slot_size));
>  
>  out:
>      kvm_slots_unlock(kml);
> diff --git a/hw/s390x/s390-virtio-ccw.c b/hw/s390x/s390-virtio-ccw.c
> index 5b6a9a4e55..0c03ffb7c7 100644
> --- a/hw/s390x/s390-virtio-ccw.c
> +++ b/hw/s390x/s390-virtio-ccw.c
> @@ -151,15 +151,6 @@ static void virtio_ccw_register_hcalls(void)
>                                     virtio_ccw_hcall_early_printk);
>  }
>  
> -/*
> - * KVM does only support memory slots up to KVM_MEM_MAX_NR_PAGES pages
> - * as the dirty bitmap must be managed by bitops that take an int as
> - * position indicator. If we have a guest beyond that we will split off
> - * new subregions. The split must happen on a segment boundary (1MB).
> - */
> -#define KVM_MEM_MAX_NR_PAGES ((1ULL << 31) - 1)
> -#define SEG_MSK (~0xfffffULL)
> -#define KVM_SLOT_MAX_BYTES ((KVM_MEM_MAX_NR_PAGES * TARGET_PAGE_SIZE) & SEG_MSK)
>  static void s390_memory_init(ram_addr_t mem_size)
>  {
>      MemoryRegion *sysmem = get_system_memory();
> diff --git a/target/s390x/kvm.c b/target/s390x/kvm.c
> index 6e814c230b..d0267da8e1 100644
> --- a/target/s390x/kvm.c
> +++ b/target/s390x/kvm.c
> @@ -347,6 +347,7 @@ int kvm_arch_init(MachineState *ms, KVMState *s)
>       */
>      /* kvm_vm_enable_cap(s, KVM_CAP_S390_AIS, 0); */
>  
> +    kvm_set_max_memslot_size(KVM_SLOT_MAX_BYTES);
>      return 0;
>  }
>  
>