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

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Date:   Wed, 8 Dec 2021 10:04:36 -0500
From:   Matthew Rosato <mjrosato@...ux.ibm.com>
To:     Niklas Schnelle <schnelle@...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 12/8/21 4:44 AM, Niklas Schnelle wrote:
> 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.

You're right of course -- I saw those changes happening as I prepared 
this series but I didn't want to delay getting comments any longer, what 
with the holidays approaching.  Of course, I didn't realize they were 
already out on the feature branch.

I suspect there is some more of this also in the code related to 
handling RPCIT.  AEN setup too.

> 
>> +	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<---
>