Re: [PATCH for-8.2] target/s390x/kvm: Simplify the GPRs, ACRs, CRs and prefix synchronization code

[Thomas Huth <thuth@redhat.com>]

On 14/08/2023 21.06, Thomas Huth wrote:
> KVM_SYNC_GPRS, KVM_SYNC_ACRS, KVM_SYNC_CRS and KVM_SYNC_PREFIX are
> available since kernel 3.10. Since we already require at least kernel
> 3.15 in the s390x KVM code, we can assume that the KVM_CAP_SYNC_REGS
> sync code is always possible for these registers, and remove the
> related checks and fallbacks via KVM_SET_REGS and KVM_GET_REGS.
> 
> Signed-off-by: Thomas Huth <thuth@redhat.com>
> ---
>   target/s390x/kvm/kvm.c | 119 ++++++++++++-----------------------------
>   1 file changed, 34 insertions(+), 85 deletions(-)

Ping! Anybody any comments on this one?

  Thomas

> diff --git a/target/s390x/kvm/kvm.c b/target/s390x/kvm/kvm.c
> index a9e5880349..ff415f7b30 100644
> --- a/target/s390x/kvm/kvm.c
> +++ b/target/s390x/kvm/kvm.c
> @@ -148,7 +148,6 @@ const KVMCapabilityInfo kvm_arch_required_capabilities[] = {
>       KVM_CAP_LAST_INFO
>   };
>   
> -static int cap_sync_regs;
>   static int cap_async_pf;
>   static int cap_mem_op;
>   static int cap_mem_op_extension;
> @@ -342,21 +341,28 @@ static void ccw_machine_class_foreach(ObjectClass *oc, void *opaque)
>   
>   int kvm_arch_init(MachineState *ms, KVMState *s)
>   {
> +    int required_caps[] = {
> +        KVM_CAP_DEVICE_CTRL,
> +        KVM_CAP_SYNC_REGS,
> +    };
> +
> +    for (int i = 0; i < ARRAY_SIZE(required_caps); i++) {
> +        if (!kvm_check_extension(s, required_caps[i])) {
> +            error_report("KVM is missing capability #%d - "
> +                         "please use kernel 3.15 or newer", required_caps[i]);
> +            return -1;
> +        }
> +    }
> +
>       object_class_foreach(ccw_machine_class_foreach, TYPE_S390_CCW_MACHINE,
>                            false, NULL);
>   
> -    if (!kvm_check_extension(kvm_state, KVM_CAP_DEVICE_CTRL)) {
> -        error_report("KVM is missing capability KVM_CAP_DEVICE_CTRL - "
> -                     "please use kernel 3.15 or newer");
> -        return -1;
> -    }
>       if (!kvm_check_extension(s, KVM_CAP_S390_COW)) {
>           error_report("KVM is missing capability KVM_CAP_S390_COW - "
>                        "unsupported environment");
>           return -1;
>       }
>   
> -    cap_sync_regs = kvm_check_extension(s, KVM_CAP_SYNC_REGS);
>       cap_async_pf = kvm_check_extension(s, KVM_CAP_ASYNC_PF);
>       cap_mem_op = kvm_check_extension(s, KVM_CAP_S390_MEM_OP);
>       cap_mem_op_extension = kvm_check_extension(s, KVM_CAP_S390_MEM_OP_EXTENSION);
> @@ -463,15 +469,15 @@ void kvm_s390_reset_vcpu_normal(S390CPU *cpu)
>   
>   static int can_sync_regs(CPUState *cs, int regs)
>   {
> -    return cap_sync_regs && (cs->kvm_run->kvm_valid_regs & regs) == regs;
> +    return (cs->kvm_run->kvm_valid_regs & regs) == regs;
>   }
>   
>   int kvm_arch_put_registers(CPUState *cs, int level)
>   {
> +    const int required_syncs = KVM_SYNC_GPRS | KVM_SYNC_ACRS |
> +                               KVM_SYNC_CRS | KVM_SYNC_PREFIX;
>       S390CPU *cpu = S390_CPU(cs);
>       CPUS390XState *env = &cpu->env;
> -    struct kvm_sregs sregs;
> -    struct kvm_regs regs;
>       struct kvm_fpu fpu = {};
>       int r;
>       int i;
> @@ -480,21 +486,16 @@ int kvm_arch_put_registers(CPUState *cs, int level)
>       cs->kvm_run->psw_addr = env->psw.addr;
>       cs->kvm_run->psw_mask = env->psw.mask;
>   
> -    if (can_sync_regs(cs, KVM_SYNC_GPRS)) {
> -        for (i = 0; i < 16; i++) {
> -            cs->kvm_run->s.regs.gprs[i] = env->regs[i];
> -            cs->kvm_run->kvm_dirty_regs |= KVM_SYNC_GPRS;
> -        }
> -    } else {
> -        for (i = 0; i < 16; i++) {
> -            regs.gprs[i] = env->regs[i];
> -        }
> -        r = kvm_vcpu_ioctl(cs, KVM_SET_REGS, &regs);
> -        if (r < 0) {
> -            return r;
> -        }
> +    g_assert((cs->kvm_run->kvm_valid_regs & required_syncs) == required_syncs);
> +    cs->kvm_run->kvm_dirty_regs |= required_syncs;
> +    for (i = 0; i < 16; i++) {
> +        cs->kvm_run->s.regs.gprs[i] = env->regs[i];
> +        cs->kvm_run->s.regs.acrs[i] = env->aregs[i];
> +        cs->kvm_run->s.regs.crs[i] = env->cregs[i];
>       }
>   
> +    cs->kvm_run->s.regs.prefix = env->psa;
> +
>       if (can_sync_regs(cs, KVM_SYNC_VRS)) {
>           for (i = 0; i < 32; i++) {
>               cs->kvm_run->s.regs.vrs[i][0] = env->vregs[i][0];
> @@ -572,25 +573,6 @@ int kvm_arch_put_registers(CPUState *cs, int level)
>           }
>       }
>   
> -    /* access registers and control registers*/
> -    if (can_sync_regs(cs, KVM_SYNC_ACRS | KVM_SYNC_CRS)) {
> -        for (i = 0; i < 16; i++) {
> -            cs->kvm_run->s.regs.acrs[i] = env->aregs[i];
> -            cs->kvm_run->s.regs.crs[i] = env->cregs[i];
> -        }
> -        cs->kvm_run->kvm_dirty_regs |= KVM_SYNC_ACRS;
> -        cs->kvm_run->kvm_dirty_regs |= KVM_SYNC_CRS;
> -    } else {
> -        for (i = 0; i < 16; i++) {
> -            sregs.acrs[i] = env->aregs[i];
> -            sregs.crs[i] = env->cregs[i];
> -        }
> -        r = kvm_vcpu_ioctl(cs, KVM_SET_SREGS, &sregs);
> -        if (r < 0) {
> -            return r;
> -        }
> -    }
> -
>       if (can_sync_regs(cs, KVM_SYNC_GSCB)) {
>           memcpy(cs->kvm_run->s.regs.gscb, env->gscb, 32);
>           cs->kvm_run->kvm_dirty_regs |= KVM_SYNC_GSCB;
> @@ -612,22 +594,15 @@ int kvm_arch_put_registers(CPUState *cs, int level)
>           cs->kvm_run->kvm_dirty_regs |= KVM_SYNC_DIAG318;
>       }
>   
> -    /* Finally the prefix */
> -    if (can_sync_regs(cs, KVM_SYNC_PREFIX)) {
> -        cs->kvm_run->s.regs.prefix = env->psa;
> -        cs->kvm_run->kvm_dirty_regs |= KVM_SYNC_PREFIX;
> -    } else {
> -        /* prefix is only supported via sync regs */
> -    }
>       return 0;
>   }
>   
>   int kvm_arch_get_registers(CPUState *cs)
>   {
> +    const int required_syncs = KVM_SYNC_GPRS | KVM_SYNC_ACRS |
> +                               KVM_SYNC_CRS | KVM_SYNC_PREFIX;
>       S390CPU *cpu = S390_CPU(cs);
>       CPUS390XState *env = &cpu->env;
> -    struct kvm_sregs sregs;
> -    struct kvm_regs regs;
>       struct kvm_fpu fpu;
>       int i, r;
>   
> @@ -635,37 +610,16 @@ int kvm_arch_get_registers(CPUState *cs)
>       env->psw.addr = cs->kvm_run->psw_addr;
>       env->psw.mask = cs->kvm_run->psw_mask;
>   
> -    /* the GPRS */
> -    if (can_sync_regs(cs, KVM_SYNC_GPRS)) {
> -        for (i = 0; i < 16; i++) {
> -            env->regs[i] = cs->kvm_run->s.regs.gprs[i];
> -        }
> -    } else {
> -        r = kvm_vcpu_ioctl(cs, KVM_GET_REGS, &regs);
> -        if (r < 0) {
> -            return r;
> -        }
> -         for (i = 0; i < 16; i++) {
> -            env->regs[i] = regs.gprs[i];
> -        }
> +    /* the GPRS, ACRS and CRS */
> +    g_assert((cs->kvm_run->kvm_valid_regs & required_syncs) == required_syncs);
> +    for (i = 0; i < 16; i++) {
> +        env->regs[i] = cs->kvm_run->s.regs.gprs[i];
> +        env->aregs[i] = cs->kvm_run->s.regs.acrs[i];
> +        env->cregs[i] = cs->kvm_run->s.regs.crs[i];
>       }
>   
> -    /* The ACRS and CRS */
> -    if (can_sync_regs(cs, KVM_SYNC_ACRS | KVM_SYNC_CRS)) {
> -        for (i = 0; i < 16; i++) {
> -            env->aregs[i] = cs->kvm_run->s.regs.acrs[i];
> -            env->cregs[i] = cs->kvm_run->s.regs.crs[i];
> -        }
> -    } else {
> -        r = kvm_vcpu_ioctl(cs, KVM_GET_SREGS, &sregs);
> -        if (r < 0) {
> -            return r;
> -        }
> -         for (i = 0; i < 16; i++) {
> -            env->aregs[i] = sregs.acrs[i];
> -            env->cregs[i] = sregs.crs[i];
> -        }
> -    }
> +    /* The prefix */
> +    env->psa = cs->kvm_run->s.regs.prefix;
>   
>       /* Floating point and vector registers */
>       if (can_sync_regs(cs, KVM_SYNC_VRS)) {
> @@ -690,11 +644,6 @@ int kvm_arch_get_registers(CPUState *cs)
>           env->fpc = fpu.fpc;
>       }
>   
> -    /* The prefix */
> -    if (can_sync_regs(cs, KVM_SYNC_PREFIX)) {
> -        env->psa = cs->kvm_run->s.regs.prefix;
> -    }
> -
>       if (can_sync_regs(cs, KVM_SYNC_ARCH0)) {
>           env->cputm = cs->kvm_run->s.regs.cputm;
>           env->ckc = cs->kvm_run->s.regs.ckc;