[Qemu-devel] Getting rid of phys_mem_set_alloc (was: Re: [PATCH V6 2/5] mem: add share parameter to memory-backend-ram)

[Cornelia Huck <cohuck@redhat.com>]

On Sun,  7 Jan 2018 14:32:21 +0200
Marcel Apfelbaum <marcel@redhat.com> wrote:

Looking at the churn below...

> diff --git a/exec.c b/exec.c
> index 4722e521d4..247f8bd0c0 100644
> --- a/exec.c
> +++ b/exec.c
> @@ -1278,7 +1278,7 @@ static int subpage_register (subpage_t *mmio, uint32_t start, uint32_t end,
>                               uint16_t section);
>  static subpage_t *subpage_init(FlatView *fv, hwaddr base);
>  
> -static void *(*phys_mem_alloc)(size_t size, uint64_t *align) =
> +static void *(*phys_mem_alloc)(size_t size, uint64_t *align, bool shared) =
>                                 qemu_anon_ram_alloc;
>  
>  /*
> @@ -1286,7 +1286,7 @@ static void *(*phys_mem_alloc)(size_t size, uint64_t *align) =
>   * Accelerators with unusual needs may need this.  Hopefully, we can
>   * get rid of it eventually.
>   */
> -void phys_mem_set_alloc(void *(*alloc)(size_t, uint64_t *align))
> +void phys_mem_set_alloc(void *(*alloc)(size_t, uint64_t *align, bool shared))
>  {
>      phys_mem_alloc = alloc;
>  }

> diff --git a/include/sysemu/kvm.h b/include/sysemu/kvm.h
> index bbf12a1723..85002ac49a 100644
> --- a/include/sysemu/kvm.h
> +++ b/include/sysemu/kvm.h
> @@ -248,7 +248,7 @@ int kvm_on_sigbus(int code, void *addr);
>  
>  /* interface with exec.c */
>  
> -void phys_mem_set_alloc(void *(*alloc)(size_t, uint64_t *align));
> +void phys_mem_set_alloc(void *(*alloc)(size_t, uint64_t *align, bool shared));
>  
>  /* internal API */
>  

> diff --git a/target/s390x/kvm.c b/target/s390x/kvm.c
> index 9b8b59f2a2..6c0fc2f89c 100644
> --- a/target/s390x/kvm.c
> +++ b/target/s390x/kvm.c
> @@ -144,7 +144,7 @@ static int cap_gs;
>  
>  static int active_cmma;
>  
> -static void *legacy_s390_alloc(size_t size, uint64_t *align);
> +static void *legacy_s390_alloc(size_t size, uint64_t *align, bool shared);
>  
>  static int kvm_s390_query_mem_limit(uint64_t *memory_limit)
>  {
> @@ -743,7 +743,7 @@ int kvm_s390_mem_op(S390CPU *cpu, vaddr addr, uint8_t ar, void *hostbuf,
>   * to grow. We also have to use MAP parameters that avoid
>   * read-only mapping of guest pages.
>   */
> -static void *legacy_s390_alloc(size_t size, uint64_t *align)
> +static void *legacy_s390_alloc(size_t size, uint64_t *align, bool shared)
>  {
>      void *mem;
>  

...I'm wondering whether we have any chance to get rid of this in the
future?

s390x/kvm is the only user:

    if (!kvm_check_extension(s, KVM_CAP_S390_GMAP)
        || !kvm_check_extension(s, KVM_CAP_S390_COW)) {
        phys_mem_set_alloc(legacy_s390_alloc);
    }

In practice, this means depending on ESOP in the host. Are there still
any machines/hypervisors without ESOP that we can reasonably expect
people to run kvm on?