linux-kernel - Re: [PATCH v2 2/2] s390/kvm: VSIE: correctly handle MVPG when in VSIE

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Message-ID: <2e409ab1-1865-d59a-dc89-2d30f2657a38@linux.ibm.com>
Date:   Thu, 4 Feb 2021 18:10:01 +0100
From:   Janosch Frank <frankja@...ux.ibm.com>
To:     Claudio Imbrenda <imbrenda@...ux.ibm.com>,
        linux-kernel@...r.kernel.org
Cc:     borntraeger@...ibm.com, david@...hat.com, kvm@...r.kernel.org,
        linux-s390@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH v2 2/2] s390/kvm: VSIE: correctly handle MVPG when in VSIE

On 2/2/21 7:00 PM, 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@...r.kernel.org
> Signed-off-by: Claudio Imbrenda <imbrenda@...ux.ibm.com>

So far the patch looks ok to me and way better to understand than v1,
good job

> ---
>  arch/s390/kvm/vsie.c | 94 +++++++++++++++++++++++++++++++++++++++++---
>  1 file changed, 89 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/s390/kvm/vsie.c b/arch/s390/kvm/vsie.c
> index 7db022141db3..2db49749e27b 100644
> --- a/arch/s390/kvm/vsie.c
> +++ b/arch/s390/kvm/vsie.c
> @@ -416,11 +416,6 @@ 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);

Magic offsets being magic
Another item for my todo list.

>  		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)
> @@ -982,6 +977,91 @@ 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;
> +	switch (reg) {
> +	case 15:
> +		return vsie_page->scb_s.gg15;
> +	case 14:
> +		return vsie_page->scb_s.gg14;
> +	default:
> +		return vcpu->run->s.regs.gprs[reg];
> +	}
> +}
> +
> +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 pei1, pei2, src, dest, mask = PAGE_MASK;
> +	u64 *pei_block = &vsie_page->scb_o->mcic;
> +	int edat, rc1, rc2;

Can use a src/dst prefix or suffix please?
1/2 is confusing.

> +	union ctlreg0 cr0;
> +
> +	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)
> +		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;
> +
> +	rc1 = kvm_s390_shadow_fault(vcpu, vsie_page->gmap, dest, &pei1);
> +	rc2 = kvm_s390_shadow_fault(vcpu, vsie_page->gmap, src, &pei2);
> +	/*
> +	 * Either everything went well, or something non-critical went wrong
> +	 * e.g. beause of a race. In either case, simply retry.
> +	 */
> +	if (rc1 == -EAGAIN || rc2 == -EAGAIN || (!rc1 && !rc2)) {
> +		retry_vsie_icpt(vsie_page);
> +		return -EAGAIN;
> +	}
> +	/* Something more serious went wrong, propagate the error */
> +	if (rc1 < 0)
> +		return rc1;
> +	if (rc2 < 0)
> +		return rc2;
> +
> +	/* The only possible suppressing exception: just deliver it */
> +	if (rc1 == PGM_TRANSLATION_SPEC || rc2 == PGM_TRANSLATION_SPEC) {
> +		clear_vsie_icpt(vsie_page);
> +		rc1 = kvm_s390_inject_program_int(vcpu, PGM_TRANSLATION_SPEC);
> +		WARN_ON_ONCE(rc1);
> +		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) {
> +		rc1 = rc1 == PGM_ASCE_TYPE ? rc1 : 0;
> +		rc2 = rc2 == PGM_ASCE_TYPE ? rc2 : 0;
> +	}
> +	if ((!rc1 || rc1 == PGM_PAGE_TRANSLATION) && (!rc2 || rc2 == PGM_PAGE_TRANSLATION)) {
> +		pei_block[0] = pei1;
> +		pei_block[1] = pei2;
> +		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 (rc1)
> +		return inject_fault(vcpu, rc1, dest, 1);
> +	if (rc2)> +		return inject_fault(vcpu, rc2, src, 0);
> +
> +	/* This should never be reached */

BUG()?

> +	return 0;
> +}
> +
>  /*
>   * Run the vsie on a shadow scb and a shadow gmap, without any further
>   * sanity checks, handling SIE faults.
> @@ -1068,6 +1148,10 @@ static int do_vsie_run(struct kvm_vcpu *vcpu, struct vsie_page *vsie_page)
>  		if ((scb_s->ipa & 0xf000) != 0xf000)
>  			scb_s->ipa += 0x1000;
>  		break;
> +	case ICPT_PARTEXEC:
> +		if (scb_s->ipa == 0xb254)
> +			rc = vsie_handle_mvpg(vcpu, vsie_page);
> +		break;
>  	}
>  	return rc;
>  }
>