Re: [PATCH 1/1] KVM: s390: fix LPSWEY handling

Claudio Imbrenda
2024-06-27T09:24:09Z

On Thu, 27 Jun 2024 11:05:20 +0200
Christian Borntraeger <borntraeger@linux.ibm.com> wrote:

> in rare cases, e.g. for injecting a machine check we do intercept all
> load PSW instructions via ICTL_LPSW. With facility 193 a new variant
> LPSWEY was added. KVM needs to handle that as well.
>
> Fixes: a3efa8429266 ("KVM: s390: gen_facilities: allow facilities 165, 193, 194 and 196")
> Reported-by: Marc Hartmayer <mhartmay@linux.ibm.com>
> Signed-off-by: Christian Borntraeger <borntraeger@linux.ibm.com>

[...]

> +static inline u64 kvm_s390_get_base_disp_siy(struct kvm_vcpu *vcpu, u8 *ar)
> +{
> + u32 base1 = vcpu->arch.sie_block->ipb >> 28;
> + u32 disp1 = ((vcpu->arch.sie_block->ipb & 0x0fff0000) >> 16) +
> + ((vcpu->arch.sie_block->ipb & 0xff00) << 4);
> +
> + /* The displacement is a 20bit _SIGNED_ value */
> + if (disp1 & 0x80000)
> + disp1+=0xfff00000;
> +
> + if (ar)
> + *ar = base1;
> +
> + return (base1 ? vcpu->run->s.regs.gprs[base1] : 0) + (long)(int)disp1;
> +}
> +
> static inline void kvm_s390_get_base_disp_sse(struct kvm_vcpu *vcpu,
> u64 *address1, u64 *address2,
> u8 *ar_b1, u8 *ar_b2)
> diff --git a/arch/s390/kvm/priv.c b/arch/s390/kvm/priv.c
> index 1be19cc9d73c..1a49b89706f8 100644
> --- a/arch/s390/kvm/priv.c
> +++ b/arch/s390/kvm/priv.c
> @@ -797,6 +797,36 @@ static int handle_lpswe(struct kvm_vcpu *vcpu)
> return 0;
> }
>
> +static int handle_lpswey(struct kvm_vcpu *vcpu)
> +{
> + psw_t new_psw;
> + u64 addr;
> + int rc;
> + u8 ar;
> +
> + vcpu->stat.instruction_lpswey++;
> +
> + if (!test_kvm_facility(vcpu->kvm, 193))
> + return kvm_s390_inject_program_int(vcpu, PGM_OPERATION);
> +
> + if (vcpu->arch.sie_block->gpsw.mask & PSW_MASK_PSTATE)
> + return kvm_s390_inject_program_int(vcpu, PGM_PRIVILEGED_OP);
> +
> + addr = kvm_s390_get_base_disp_siy(vcpu, &ar);
> + if (addr & 7)
> + return kvm_s390_inject_program_int(vcpu, PGM_SPECIFICATION);
> +
> + rc = read_guest(vcpu, addr, ar, &new_psw, sizeof(new_psw));
> + if (rc)
> + return kvm_s390_inject_prog_cond(vcpu, rc);
> +
> + vcpu->arch.sie_block->gpsw = new_psw;
> + if (!is_valid_psw(&vcpu->arch.sie_block->gpsw))
> + return kvm_s390_inject_program_int(vcpu, PGM_SPECIFICATION);
> +
> + return 0;
> +}

looks quite straightforward, but you duplicated most of handle_lpswe.
it would probably be cleaner to abstract the "load psw" logic, and
convert handle_lpswe{,y} to be wrappers around it, something like

static int _handle_load_psw(struct kvm_vcpu *vcpu, unsigned long
pswaddr)

which can then contain the old code from the "if (addr & 7)" to the end
of the function.

I think it would look cleaner, but I don't have a super strong opinion
about it