linux-kernel - Re: [PATCH 20/32] KVM: s390: pci: provide routines for enabling/disabling interpretation

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Date:   Wed, 08 Dec 2021 10:44:19 +0100
From:   Niklas Schnelle <schnelle@...ux.ibm.com>
To:     Matthew Rosato <mjrosato@...ux.ibm.com>, linux-s390@...r.kernel.org
Cc:     alex.williamson@...hat.com, cohuck@...hat.com,
        farman@...ux.ibm.com, pmorel@...ux.ibm.com,
        borntraeger@...ux.ibm.com, hca@...ux.ibm.com, gor@...ux.ibm.com,
        gerald.schaefer@...ux.ibm.com, agordeev@...ux.ibm.com,
        frankja@...ux.ibm.com, david@...hat.com, imbrenda@...ux.ibm.com,
        vneethv@...ux.ibm.com, oberpar@...ux.ibm.com, freude@...ux.ibm.com,
        thuth@...hat.com, pasic@...ux.ibm.com, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 20/32] KVM: s390: pci: provide routines for
 enabling/disabling interpretation

On Tue, 2021-12-07 at 15:57 -0500, Matthew Rosato wrote:
> These routines will be wired into the vfio_pci_zdev ioctl handlers to
> respond to requests to enable / disable a device for zPCI Load/Store
> interpretation.
> 
> The first time such a request is received, enable the necessary facilities
> for the guest.
> 
> Signed-off-by: Matthew Rosato <mjrosato@...ux.ibm.com>
> ---
>  arch/s390/include/asm/kvm_pci.h |  4 ++
>  arch/s390/kvm/pci.c             | 91 +++++++++++++++++++++++++++++++++
>  arch/s390/pci/pci.c             |  3 ++
>  3 files changed, 98 insertions(+)
> 
> diff --git a/arch/s390/include/asm/kvm_pci.h b/arch/s390/include/asm/kvm_pci.h
> index 3e491a39704c..5d6283acb54c 100644
> --- a/arch/s390/include/asm/kvm_pci.h
> 
---8<---
> 		return rc;
> +	}
> +
> +	/*
> +	 * Store information about the identity of the kvm guest allowed to
> +	 * access this device via interpretation to be used by host CLP
> +	 */
> +	zdev->gd = gd;
> +
> +	rc = zpci_enable_device(zdev);
> +	if (rc)
> +		goto err;
> +
> +	/* Re-register the IOMMU that was already created */
> +	rc = zpci_register_ioat(zdev, 0, zdev->start_dma, zdev->end_dma,
> +				(u64)zdev->dma_table);

The zdev->dma_table is a virtual address but we need an absolute
address in the MPCIFC so the above should use
virt_to_phys(zdev->dma_table) to be compatible with future V != R
kernel memory. As of now since virtual and absolute kernel addresses
are the same this is not a bug and we've had this (wrong) pattern in
the rest of the code but let's get it righht here from the start.

See also my commit "s390/pci: use physical addresses in DMA tables"
that is currently in the s390 feature branch.

> +	if (rc)
> +		goto err;
> +
> +	return rc;
> +
> +err:
> +	zdev->gd = 0;
> +	return rc;
> +}
> +EXPORT_SYMBOL_GPL(kvm_s390_pci_interp_enable);
> +
> +int kvm_s390_pci_interp_disable(struct zpci_dev *zdev)
> +{
> +	int rc;
> +
> +	if (zdev->gd == 0)
> +		return -EINVAL;
> +
> +	/* Remove the host CLP guest designation */
> +	zdev->gd = 0;
> +
> +	if (zdev_enabled(zdev)) {
> +		rc = zpci_disable_device(zdev);
> +		if (rc)
> +			return rc;
> +	}
> +
> +	rc = zpci_enable_device(zdev);
> +	if (rc)
> +		return rc;
> +
> +	/* Re-register the IOMMU that was already created */
> +	rc = zpci_register_ioat(zdev, 0, zdev->start_dma, zdev->end_dma,
> +				(u64)zdev->dma_table);

Same as above

> +
> +	return rc;
> +}
> +EXPORT_SYMBOL_GPL(kvm_s390_pci_interp_disable);
> +
> 
---8<---