Re: [PATCH RFC V2 31/37] physmem,gdbstub: Common helping funcs/changes to *unrealize* vCPU

["Philippe Mathieu-Daudé" <philmd@linaro.org>]

Hi Salil,

On 26/9/23 12:04, Salil Mehta wrote:
> Supporting vCPU Hotplug for ARM arch also means introducing new functionality of
> unrealizing the ARMCPU. This requires some new common functions.
> 
> Defining them as part of architecture independent change so that this code could
> be reused by other interested parties.
> 
> Signed-off-by: Salil Mehta <salil.mehta@huawei.com>
> ---
>   gdbstub/gdbstub.c         | 13 +++++++++++++
>   include/exec/cpu-common.h |  8 ++++++++
>   include/exec/gdbstub.h    |  1 +
>   include/hw/core/cpu.h     |  1 +
>   softmmu/physmem.c         | 25 +++++++++++++++++++++++++
>   5 files changed, 48 insertions(+)


> diff --git a/include/hw/core/cpu.h b/include/hw/core/cpu.h
> index dab572c9bd..ffd815a0d8 100644
> --- a/include/hw/core/cpu.h
> +++ b/include/hw/core/cpu.h
> @@ -366,6 +366,7 @@ struct CPUState {
>       QSIMPLEQ_HEAD(, qemu_work_item) work_list;
>   
>       CPUAddressSpace *cpu_ases;
> +    int cpu_ases_ref_count;
>       int num_ases;
>       AddressSpace *as;
>       MemoryRegion *memory;
> diff --git a/softmmu/physmem.c b/softmmu/physmem.c
> index 3df73542e1..a93ae783af 100644
> --- a/softmmu/physmem.c
> +++ b/softmmu/physmem.c
> @@ -762,6 +762,7 @@ void cpu_address_space_init(CPUState *cpu, int asidx,
>   
>       if (!cpu->cpu_ases) {
>           cpu->cpu_ases = g_new0(CPUAddressSpace, cpu->num_ases);
> +        cpu->cpu_ases_ref_count = cpu->num_ases;
>       }
>   
>       newas = &cpu->cpu_ases[asidx];
> @@ -775,6 +776,30 @@ void cpu_address_space_init(CPUState *cpu, int asidx,
>       }
>   }
>   
> +void cpu_address_space_destroy(CPUState *cpu, int asidx)
> +{
> +    CPUAddressSpace *cpuas;
> +
> +    assert(asidx < cpu->num_ases);
> +    assert(asidx == 0 || !kvm_enabled());
> +    assert(cpu->cpu_ases);
> +
> +    cpuas = &cpu->cpu_ases[asidx];
> +    if (tcg_enabled()) {
> +        memory_listener_unregister(&cpuas->tcg_as_listener);
> +    }
> +
> +    address_space_destroy(cpuas->as);
> +    g_free_rcu(cpuas->as, rcu);
> +
> +    if (cpu->cpu_ases_ref_count == 1) {
> +        g_free(cpu->cpu_ases);
> +        cpu->cpu_ases = NULL;
> +    }
> +
> +    cpu->cpu_ases_ref_count--;

See Richard comment from:
https://lore.kernel.org/qemu-devel/594b2550-9a73-684f-6e54-29401dc6cd7a@linaro.org/

"I think it would be better to destroy all address spaces at once,
"so that you don't need  to invent a reference count that isn't used
"for anything else.

> +}
> +
>   AddressSpace *cpu_get_address_space(CPUState *cpu, int asidx)
>   {
>       /* Return the AddressSpace corresponding to the specified index */