Re: [Qemu-devel] [PATCH] target-i386: Sanity check host processor physical address width

[Bandan Das <bsd@redhat.com>]

Igor Mammedov <imammedo@redhat.com> writes:

> On Wed, 08 Jul 2015 18:42:01 -0400
> Bandan Das <bsd@redhat.com> wrote:
>
>> 
>> If a Linux guest is assigned more memory than is supported
>> by the host processor, the guest is unable to boot. That
>> is expected, however, there's no message indicating the user
>> what went wrong. This change prints a message to stderr if
>> KVM has the corresponding capability.
>> 
>> Reported-by: Laszlo Ersek <lersek@redhat.com>
>> Signed-off-by: Bandan Das <bsd@redhat.com>
>> ---
>>  linux-headers/linux/kvm.h | 1 +
>>  target-i386/kvm.c         | 6 ++++++
>>  2 files changed, 7 insertions(+)
>> 
>> diff --git a/linux-headers/linux/kvm.h b/linux-headers/linux/kvm.h
>> index 3bac873..6afad49 100644
>> --- a/linux-headers/linux/kvm.h
>> +++ b/linux-headers/linux/kvm.h
>> @@ -817,6 +817,7 @@ struct kvm_ppc_smmu_info {
>>  #define KVM_CAP_DISABLE_QUIRKS 116
>>  #define KVM_CAP_X86_SMM 117
>>  #define KVM_CAP_MULTI_ADDRESS_SPACE 118
>> +#define KVM_CAP_PHY_ADDR_WIDTH 119
>>  
>>  #ifdef KVM_CAP_IRQ_ROUTING
>>  
>> diff --git a/target-i386/kvm.c b/target-i386/kvm.c
>> index 066d03d..66e3448 100644
>> --- a/target-i386/kvm.c
>> +++ b/target-i386/kvm.c
>> @@ -892,6 +892,7 @@ int kvm_arch_init(MachineState *ms, KVMState *s)
>>      uint64_t shadow_mem;
>>      int ret;
>>      struct utsname utsname;
>> +    int max_phys_bits;
>>  
>>      ret = kvm_get_supported_msrs(s);
>>      if (ret < 0) {
>> @@ -945,6 +946,11 @@ int kvm_arch_init(MachineState *ms, KVMState *s)
>>          }
>>      }
>>  
>> +    max_phys_bits = kvm_check_extension(s, KVM_CAP_PHY_ADDR_WIDTH);
> max_phys_bits seems generic enough and could be applied to other targets
> as well.

I am a little clueless about other targets but is figuring this out from userspace
as simple as it's on x86 (cpuid)? If not, then I agree, this could be made a generic
value.

Bandan

> making it a property of machine, would make accessing/manipulating it easier.
> define default value for machine/TCG mode and when KVM is enabled
> it would override/set its own limit.
>
> then any board could easily access machine->max_gpa to make board specific
> checks.
>
>> +    if (max_phys_bits && (1ULL << max_phys_bits) <= ram_size)
>> +        fprintf(stderr, "Warning: The amount of memory assigned to the guest "
>> +            "is more than that supported by the host CPU(s). Guest may be unstable.\n");
>> +
>>      if (kvm_check_extension(s, KVM_CAP_X86_SMM)) {
>>          smram_machine_done.notify = register_smram_listener;
>>          qemu_add_machine_init_done_notifier(&smram_machine_done);