Re: [PATCH v4 2/2] s390/kvm: VSIE: correctly handle MVPG when in VSIE

David Hildenbrand
2021-02-25T19:16:29Z

On 23.02.21 20:13, Claudio Imbrenda wrote:
> Correctly handle the MVPG instruction when issued by a VSIE guest.
>
> Fixes: a3508fbe9dc6d ("KVM: s390: vsie: initial support for nested virtualization")
> Cc: stable@vger.kernel.org
> Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
> Acked-by: Janosch Frank <frankja@linux.ibm.com>
> ---
> arch/s390/kvm/vsie.c | 93 +++++++++++++++++++++++++++++++++++++++++---
> 1 file changed, 88 insertions(+), 5 deletions(-)
>
> diff --git a/arch/s390/kvm/vsie.c b/arch/s390/kvm/vsie.c
> index 78b604326016..dbf4241bc2dc 100644
> --- a/arch/s390/kvm/vsie.c
> +++ b/arch/s390/kvm/vsie.c
> @@ -417,11 +417,6 @@ static void unshadow_scb(struct kvm_vcpu *vcpu, struct vsie_page *vsie_page)
> memcpy((void *)((u64)scb_o + 0xc0),
> (void *)((u64)scb_s + 0xc0), 0xf0 - 0xc0);
> break;
> - case ICPT_PARTEXEC:
> - /* MVPG only */
> - memcpy((void *)((u64)scb_o + 0xc0),
> - (void *)((u64)scb_s + 0xc0), 0xd0 - 0xc0);
> - break;
> }
>
> if (scb_s->ihcpu != 0xffffU)
> @@ -983,6 +978,90 @@ static int handle_stfle(struct kvm_vcpu *vcpu, struct vsie_page *vsie_page)
> return 0;
> }
>
> +static u64 vsie_get_register(struct kvm_vcpu *vcpu, struct vsie_page *vsie_page, u8 reg)
> +{
> + reg &= 0xf;

Nit, I'd mask of that value in the caller where you extract it from the ipb.

...

> +static int vsie_handle_mvpg(struct kvm_vcpu *vcpu, struct vsie_page *vsie_page)
> +{
> + struct kvm_s390_sie_block *scb_s = &vsie_page->scb_s;
> + unsigned long pei_dest, pei_src, src, dest, mask = PAGE_MASK;
> + u64 *pei_block = &vsie_page->scb_o->mcic;
> + int edat, rc_dest, rc_src;
> + union ctlreg0 cr0;

...

const uint8_t r1 = (scb_s->ipb >> 16) & 0xf;
const uint8_t r3 = (scb_s->ipb >> 20) & 0xf;

(note: r1/r3 is just a guess ;) - and having the actual identifiers here
will make the code easier to understand)

> +
> + cr0.val = vcpu->arch.sie_block->gcr[0];
> + edat = cr0.edat && test_kvm_facility(vcpu->kvm, 8);
> + if (psw_bits(scb_s->gpsw).eaba == PSW_BITS_AMODE_24BIT)

What about factoring out that masking like

kvm_s390_logical_to_effective()

introduce

vsie_logical_to_effective()

to handle that.

> + mask = 0xfff000;
> + else if (psw_bits(scb_s->gpsw).eaba == PSW_BITS_AMODE_31BIT)
> + mask = 0x7ffff000;
> +
> + dest = vsie_get_register(vcpu, vsie_page, scb_s->ipb >> 16) & mask;
> + src = vsie_get_register(vcpu, vsie_page, scb_s->ipb >> 20) & mask;
> +
> + rc_dest = kvm_s390_shadow_fault(vcpu, vsie_page->gmap, dest, &pei_dest);
> + rc_src = kvm_s390_shadow_fault(vcpu, vsie_page->gmap, src, &pei_src);
> + /*
> + * Either everything went well, or something non-critical went wrong
> + * e.g. beause of a race. In either case, simply retry.

s/beause/because/

> + */
> + if (rc_dest == -EAGAIN || rc_src == -EAGAIN || (!rc_dest && !rc_src)) {
> + retry_vsie_icpt(vsie_page);
> + return -EAGAIN;

I remember, because of the retry_vsie_icpt() you can simply return 0.
Whatever you prefer.

> + }
> + /* Something more serious went wrong, propagate the error */
> + if (rc_dest < 0)
> + return rc_dest;
> + if (rc_src < 0)
> + return rc_src;
> +
> + /* The only possible suppressing exception: just deliver it */
> + if (rc_dest == PGM_TRANSLATION_SPEC || rc_src == PGM_TRANSLATION_SPEC) {
> + clear_vsie_icpt(vsie_page);
> + rc_dest = kvm_s390_inject_program_int(vcpu, PGM_TRANSLATION_SPEC);
> + WARN_ON_ONCE(rc_dest);
> + return 1;
> + }
> +
> + /*
> + * Forward the PEI intercept to the guest if it was a page fault, or
> + * also for segment and region table faults if EDAT applies.
> + */
> + if (edat) {
> + rc_dest = rc_dest == PGM_ASCE_TYPE ? rc_dest : 0;
> + rc_src = rc_src == PGM_ASCE_TYPE ? rc_src : 0;
> + } else {
> + rc_dest = rc_dest != PGM_PAGE_TRANSLATION ? rc_dest : 0;
> + rc_src = rc_src != PGM_PAGE_TRANSLATION ? rc_src : 0;
> + }
> + if (!rc_dest && !rc_src) {
> + pei_block[0] = pei_dest;
> + pei_block[1] = pei_src;
> + return 1;
> + }
> +
> + retry_vsie_icpt(vsie_page);
> +
> + /*
> + * The host has edat, and the guest does not, or it was an ASCE type
> + * exception. The host needs to inject the appropriate DAT interrupts
> + * into the guest.
> + */
> + if (rc_dest)
> + return inject_fault(vcpu, rc_dest, dest, 1);
> + return inject_fault(vcpu, rc_src, src, 0);

The rc_dest and rc_src handling towards the end is a little confusing,
but I have no real suggestion to make it easier to digest.

Only some suggestions to make the code a bit nicer to read. Apart from
that LGTM.

Reviewed-by: David Hildenbrand <david@redhat.com>

--
Thanks,

David / dhildenb