Re: [PATCH 1/2] i386/cpu: Enable SMM cpu addressspace

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

On 29/7/25 07:40, Xiaoyao Li wrote:
> Kirill Martynov reported assertation in cpu_asidx_from_attrs() being hit
> when x86_cpu_dump_state() is called to dump the CPU state[*]. It happens
> when the CPU is in SMM and KVM emulation failure due to misbehaving
> guest.
> 
> The root cause is that QEMU i386 never enables the SMM addressspace for cpu

"address space"

> since kvm SMM support has been added.
> 
> Enable the SMM cpu address space under KVM when the SMM is enabled for
> the x86machine.
> 
> [*] https://lore.kernel.org/qemu-devel/20250523154431.506993-1-stdcalllevi@yandex-team.ru/
> 
> Reported-by: Kirill Martynov <stdcalllevi@yandex-team.ru>
> Signed-off-by: Xiaoyao Li <xiaoyao.li@intel.com>
> ---
>   system/physmem.c          |  5 -----
>   target/i386/kvm/kvm-cpu.c | 10 ++++++++++
>   target/i386/kvm/kvm.c     |  5 +++++
>   3 files changed, 15 insertions(+), 5 deletions(-)
> 
> diff --git a/system/physmem.c b/system/physmem.c
> index 130c148ffb5c..76e1c33aab5c 100644
> --- a/system/physmem.c
> +++ b/system/physmem.c
> @@ -795,9 +795,6 @@ void cpu_address_space_init(CPUState *cpu, int asidx,
>           cpu->as = as;
>       }
>   
> -    /* KVM cannot currently support multiple address spaces. */
> -    assert(asidx == 0 || !kvm_enabled());
> -
>       if (!cpu->cpu_ases) {
>           cpu->cpu_ases = g_new0(CPUAddressSpace, cpu->num_ases);
>           cpu->cpu_ases_count = cpu->num_ases;
> @@ -820,8 +817,6 @@ void cpu_address_space_destroy(CPUState *cpu, int asidx)
>   
>       assert(cpu->cpu_ases);
>       assert(asidx >= 0 && asidx < cpu->num_ases);
> -    /* KVM cannot currently support multiple address spaces. */
> -    assert(asidx == 0 || !kvm_enabled());
>   
>       cpuas = &cpu->cpu_ases[asidx];
>       if (tcg_enabled()) {
> diff --git a/target/i386/kvm/kvm-cpu.c b/target/i386/kvm/kvm-cpu.c
> index 89a795365945..aa657c2a4627 100644
> --- a/target/i386/kvm/kvm-cpu.c
> +++ b/target/i386/kvm/kvm-cpu.c
> @@ -13,6 +13,7 @@
>   #include "qapi/error.h"
>   #include "system/system.h"
>   #include "hw/boards.h"
> +#include "hw/i386/x86.h"
>   
>   #include "kvm_i386.h"
>   #include "accel/accel-cpu-target.h"
> @@ -91,6 +92,15 @@ static bool kvm_cpu_realizefn(CPUState *cs, Error **errp)
>           kvm_set_guest_phys_bits(cs);
>       }
>   
> +    /*
> +     * When SMM is enabled, there is 2 address spaces. Otherwise only 1.
> +     *
> +     * Only init address space 0 here, the second one for SMM is initialized at
> +     * register_smram_listener() after machine init done.
> +     */
> +    cs->num_ases = x86_machine_is_smm_enabled(X86_MACHINE(current_machine)) ? 2 : 1;
> +    cpu_address_space_init(cs, 0, "cpu-mmeory", cs->memory);

Typo "memory".

> +
>       return true;
>   }
>   
> diff --git a/target/i386/kvm/kvm.c b/target/i386/kvm/kvm.c
> index 369626f8c8d7..47fb5c673c8e 100644
> --- a/target/i386/kvm/kvm.c
> +++ b/target/i386/kvm/kvm.c
> @@ -2704,6 +2704,7 @@ static MemoryRegion smram_as_mem;
>   
>   static void register_smram_listener(Notifier *n, void *unused)
>   {
> +    CPUState *cpu;
>       MemoryRegion *smram =
>           (MemoryRegion *) object_resolve_path("/machine/smram", NULL);
>   
> @@ -2728,6 +2729,10 @@ static void register_smram_listener(Notifier *n, void *unused)
>       address_space_init(&smram_address_space, &smram_as_root, "KVM-SMRAM");
>       kvm_memory_listener_register(kvm_state, &smram_listener,
>                                    &smram_address_space, 1, "kvm-smram");
> +
> +    CPU_FOREACH(cpu) {
> +        cpu_address_space_init(cpu, 1, "cpu-smm", &smram_as_root);
> +    }
>   }
>   
>   static void *kvm_msr_energy_thread(void *data)