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

[Paolo Bonzini]

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
#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?

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;
>       default:
>           /* reserved values: zero */
> diff --git a/target/i386/sev-stub.c b/target/i386/sev-stub.c
> deleted file mode 100644
> index 8eae5d2fa8d..00000000000
> --- a/target/i386/sev-stub.c
> +++ /dev/null
> @@ -1,36 +0,0 @@
> -/*
> - * QEMU SEV stub
> - *
> - * Copyright Advanced Micro Devices 2018
> - *
> - * Authors:
> - *      Brijesh Singh <brijesh.singh@amd.com>
> - *
> - * This work is licensed under the terms of the GNU GPL, version 2 or later.
> - * See the COPYING file in the top-level directory.
> - *
> - */
> -
> -#include "qemu/osdep.h"
> -#include "qapi/error.h"
> -#include "sev_i386.h"
> -
> -bool sev_enabled(void)
> -{
> -    return false;
> -}
> -
> -uint32_t sev_get_cbit_position(void)
> -{
> -    return 0;
> -}
> -
> -uint32_t sev_get_reduced_phys_bits(void)
> -{
> -    return 0;
> -}
> -
> -bool sev_es_enabled(void)
> -{
> -    return false;
> -}
> diff --git a/target/i386/meson.build b/target/i386/meson.build
> index a4f45c3ec1d..ae38dc95635 100644
> --- a/target/i386/meson.build
> +++ b/target/i386/meson.build
> @@ -6,7 +6,7 @@
>     'xsave_helper.c',
>     'cpu-dump.c',
>   ))
> -i386_ss.add(when: 'CONFIG_SEV', if_true: files('host-cpu.c'), if_false: 
> files('sev-stub.c'))
> +i386_ss.add(when: 'CONFIG_SEV', if_true: files('host-cpu.c'))
>   
>   # x86 cpu type
>   i386_ss.add(when: 'CONFIG_KVM', if_true: files('host-cpu.c'))