linux-kernel - Re: [PATCH v1 2/2] s390/kvm: VSIE: fix MVPG handling for prefixing and MSO

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Date:   Mon, 22 Mar 2021 10:55:46 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Claudio Imbrenda <imbrenda@...ux.ibm.com>,
        linux-kernel@...r.kernel.org
Cc:     borntraeger@...ibm.com, frankja@...ux.ibm.com, cohuck@...hat.com,
        kvm@...r.kernel.org, linux-s390@...r.kernel.org,
        stable@...r.kernel.org
Subject: Re: [PATCH v1 2/2] s390/kvm: VSIE: fix MVPG handling for prefixing
 and MSO

On 19.03.21 20:33, Claudio Imbrenda wrote:
> Prefixing needs to be applied to the guest real address to translate it
> into a guest absolute address.
> 
> The value of MSO needs to be added to a guest-absolute address in order to
> obtain the host-virtual.
> 
> Fixes: 223ea46de9e79 ("s390/kvm: VSIE: correctly handle MVPG when in VSIE")
> Cc: stable@...r.kernel.org
> Signed-off-by: Claudio Imbrenda <imbrenda@...ux.ibm.com>
> ---
>   arch/s390/kvm/vsie.c | 10 +++++++---
>   1 file changed, 7 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/s390/kvm/vsie.c b/arch/s390/kvm/vsie.c
> index 48aab6290a77..92864f9b3d84 100644
> --- a/arch/s390/kvm/vsie.c
> +++ b/arch/s390/kvm/vsie.c
> @@ -1002,7 +1002,7 @@ static u64 vsie_get_register(struct kvm_vcpu *vcpu, struct vsie_page *vsie_page,
>   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;
> +	unsigned long pei_dest, pei_src, r1, r2, src, dest, mask, mso, prefix;
>   	u64 *pei_block = &vsie_page->scb_o->mcic;
>   	int edat, rc_dest, rc_src;
>   	union ctlreg0 cr0;
> @@ -1010,9 +1010,13 @@ static int vsie_handle_mvpg(struct kvm_vcpu *vcpu, struct vsie_page *vsie_page)
>   	cr0.val = vcpu->arch.sie_block->gcr[0];
>   	edat = cr0.edat && test_kvm_facility(vcpu->kvm, 8);
>   	mask = _kvm_s390_logical_to_effective(&scb_s->gpsw, PAGE_MASK);
> +	mso = READ_ONCE(vsie_page->scb_o->mso) & ~(1UL << 20);

I think we should use the one stored in the shadow page - this is what 
the SIE saw and will see when retrying.

> +	prefix = scb_s->prefix << GUEST_PREFIX_SHIFT;
>   
> -	dest = vsie_get_register(vcpu, vsie_page, scb_s->ipb >> 16) & mask;
> -	src = vsie_get_register(vcpu, vsie_page, scb_s->ipb >> 20) & mask;
> +	r1 = vsie_get_register(vcpu, vsie_page, scb_s->ipb >> 16);
> +	r2 = vsie_get_register(vcpu, vsie_page, scb_s->ipb >> 20);

Just reuse dest and src here?

> +	dest = _kvm_s390_real_to_abs(prefix, r1 & mask) + mso;
> +	src = _kvm_s390_real_to_abs(prefix, r2 & mask) + mso;
>   
>   	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);
> 

Apart from that, looks good to me.

-- 
Thanks,

David / dhildenb