Re: [PATCH v3 13/22] target/i386/sev: Remove stubs by using code elision

[Philippe Mathieu-Daudé]

On 10/4/21 10:19, Paolo Bonzini wrote:
> On 02/10/21 14:53, Philippe Mathieu-Daudé wrote:
>> Only declare sev_enabled() and sev_es_enabled() when CONFIG_SEV is
>> set, to allow the compiler to elide unused code. Remove unnecessary
>> stubs.
>>
>> Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
>> ---
>>   include/sysemu/sev.h    | 14 +++++++++++++-
>>   target/i386/sev_i386.h  |  3 ---
>>   target/i386/cpu.c       | 16 +++++++++-------
>>   target/i386/sev-stub.c  | 36 ------------------------------------
>>   target/i386/meson.build |  2 +-
>>   5 files changed, 23 insertions(+), 48 deletions(-)
>>   delete mode 100644 target/i386/sev-stub.c
>>
>> diff --git a/include/sysemu/sev.h b/include/sysemu/sev.h
>> index a329ed75c1c..f5c625bb3b3 100644
>> --- a/include/sysemu/sev.h
>> +++ b/include/sysemu/sev.h
>> @@ -14,9 +14,21 @@
>>   #ifndef QEMU_SEV_H
>>   #define QEMU_SEV_H
>>   -#include "sysemu/kvm.h"
>> +#ifndef CONFIG_USER_ONLY
>> +#include CONFIG_DEVICES /* CONFIG_SEV */
>> +#endif
>>   +#ifdef CONFIG_SEV
>>   bool sev_enabled(void);
>> +bool sev_es_enabled(void);
>> +#else
>> +#define sev_enabled() 0
>> +#define sev_es_enabled() 0
>> +#endif
> 
> This means that sev.h can only be included from target-specific files.
> 
> An alternative could be:
> 
> #ifdef NEED_CPU_H
> # include CONFIG_DEVICES

<command-line>: fatal error: x86_64-linux-user-config-devices.h: No such
file or directory

> #endif
> 
> #if defined NEED_CPU_H && !defined CONFIG_SEV
> # define sev_enabled() 0
> # define sev_es_enabled() 0
> #else
> bool sev_enabled(void);
> bool sev_es_enabled(void);
> #endif
> 
> ... but in fact sysemu/sev.h _is_ only used from x86-specific files. So
> should it be moved to include/hw/i386, and even merged with
> target/i386/sev_i386.h?  Do we need two files?

No clue, I don't think we need. Brijesh?

> 
> Thanks,
> 
> Paolo
> 
>> +uint32_t sev_get_cbit_position(void);
>> +uint32_t sev_get_reduced_phys_bits(void);
>> +
>>   int sev_kvm_init(ConfidentialGuestSupport *cgs, Error **errp);
>>     #endif
>> diff --git a/target/i386/sev_i386.h b/target/i386/sev_i386.h
>> index 0798ab3519a..2d9a1a0112e 100644
>> --- a/target/i386/sev_i386.h
>> +++ b/target/i386/sev_i386.h
>> @@ -24,10 +24,7 @@
>>   #define SEV_POLICY_DOMAIN       0x10
>>   #define SEV_POLICY_SEV          0x20
>>   -extern bool sev_es_enabled(void);
>>   extern SevInfo *sev_get_info(void);
>> -extern uint32_t sev_get_cbit_position(void);
>> -extern uint32_t sev_get_reduced_phys_bits(void);
>>   extern char *sev_get_launch_measurement(void);
>>   extern SevCapability *sev_get_capabilities(Error **errp);
>>   extern SevAttestationReport *
>> diff --git a/target/i386/cpu.c b/target/i386/cpu.c
>> index e169a01713d..27992bdc9f8 100644
>> --- a/target/i386/cpu.c
>> +++ b/target/i386/cpu.c
>> @@ -25,8 +25,8 @@
>>   #include "tcg/helper-tcg.h"
>>   #include "sysemu/reset.h"
>>   #include "sysemu/hvf.h"
>> +#include "sysemu/sev.h"
>>   #include "kvm/kvm_i386.h"
>> -#include "sev_i386.h"
>>   #include "qapi/error.h"
>>   #include "qapi/qapi-visit-machine.h"
>>   #include "qapi/qmp/qerror.h"
>> @@ -38,6 +38,7 @@
>>   #include "exec/address-spaces.h"
>>   #include "hw/boards.h"
>>   #include "hw/i386/sgx-epc.h"
>> +#include "sev_i386.h"
>>   #endif
>>     #include "disas/capstone.h"
>> @@ -5764,12 +5765,13 @@ void cpu_x86_cpuid(CPUX86State *env, uint32_t
>> index, uint32_t count,
>>           *edx = 0;
>>           break;
>>       case 0x8000001F:
>> -        *eax = sev_enabled() ? 0x2 : 0;
>> -        *eax |= sev_es_enabled() ? 0x8 : 0;
>> -        *ebx = sev_get_cbit_position();
>> -        *ebx |= sev_get_reduced_phys_bits() << 6;
>> -        *ecx = 0;
>> -        *edx = 0;
>> +        *eax = *ebx = *ecx = *edx = 0;
>> +        if (sev_enabled()) {
>> +            *eax = 0x2;
>> +            *eax |= sev_es_enabled() ? 0x8 : 0;
>> +            *ebx = sev_get_cbit_position();
>> +            *ebx |= sev_get_reduced_phys_bits() << 6;
>> +        }
>>           break;