Re: [PATCH v7 51/52] i386/tdx: Validate phys_bits against host value

[Xiaoyao Li <xiaoyao.li@intel.com>]

On 2/1/2025 2:27 AM, Paolo Bonzini wrote:
> On Fri, Jan 24, 2025 at 2:40 PM Xiaoyao Li <xiaoyao.li@intel.com> wrote:
>>
>> For TDX guest, the phys_bits is not configurable and can only be
>> host/native value.
>>
>> Validate phys_bits inside tdx_check_features().
> 
> Hi Xiaoyao,
> 
> to avoid
> 
> qemu-kvm: TDX requires guest CPU physical bits (48) to match host CPU
> physical bits (52)
> 
> I need options like
> 
> -cpu host,phys-bits=52,guest-phys-bits=52,host-phys-bits-limit=52,-kvm-asyncpf-int
> 
> to start a TDX guest, is that intentional?

"-cpu host" should be sufficient and should not hit the error.

why did you get "guest CPU physical bits (48)"?

> Thanks,
> 
> Paolo
> 
>> Signed-off-by: Xiaoyao Li <xiaoyao.li@intel.com>
>> ---
>>   target/i386/host-cpu.c | 2 +-
>>   target/i386/host-cpu.h | 1 +
>>   target/i386/kvm/tdx.c  | 8 ++++++++
>>   3 files changed, 10 insertions(+), 1 deletion(-)
>>
>> diff --git a/target/i386/host-cpu.c b/target/i386/host-cpu.c
>> index 3e4e85e729c8..8a15af458b05 100644
>> --- a/target/i386/host-cpu.c
>> +++ b/target/i386/host-cpu.c
>> @@ -15,7 +15,7 @@
>>   #include "system/system.h"
>>
>>   /* Note: Only safe for use on x86(-64) hosts */
>> -static uint32_t host_cpu_phys_bits(void)
>> +uint32_t host_cpu_phys_bits(void)
>>   {
>>       uint32_t eax;
>>       uint32_t host_phys_bits;
>> diff --git a/target/i386/host-cpu.h b/target/i386/host-cpu.h
>> index 6a9bc918baa4..b97ec01c9bec 100644
>> --- a/target/i386/host-cpu.h
>> +++ b/target/i386/host-cpu.h
>> @@ -10,6 +10,7 @@
>>   #ifndef HOST_CPU_H
>>   #define HOST_CPU_H
>>
>> +uint32_t host_cpu_phys_bits(void);
>>   void host_cpu_instance_init(X86CPU *cpu);
>>   void host_cpu_max_instance_init(X86CPU *cpu);
>>   bool host_cpu_realizefn(CPUState *cs, Error **errp);
>> diff --git a/target/i386/kvm/tdx.c b/target/i386/kvm/tdx.c
>> index bb75eb06dad9..c906a76c4c0e 100644
>> --- a/target/i386/kvm/tdx.c
>> +++ b/target/i386/kvm/tdx.c
>> @@ -24,6 +24,7 @@
>>
>>   #include "cpu.h"
>>   #include "cpu-internal.h"
>> +#include "host-cpu.h"
>>   #include "hw/i386/e820_memory_layout.h"
>>   #include "hw/i386/x86.h"
>>   #include "hw/i386/tdvf.h"
>> @@ -838,6 +839,13 @@ static int tdx_check_features(X86ConfidentialGuest *cg, CPUState *cs)
>>           return -1;
>>       }
>>
>> +    if (cpu->phys_bits != host_cpu_phys_bits()) {
>> +        error_report("TDX requires guest CPU physical bits (%u) "
>> +                     "to match host CPU physical bits (%u)",
>> +                     cpu->phys_bits, host_cpu_phys_bits());
>> +        exit(1);
>> +    }
>> +
>>       return 0;
>>   }
>>
>> --
>> 2.34.1
>>
> 
>