Re: [PATCH v2 20/30] KVM: s390: pci: provide routines for enabling/disabling IOAT assist

Pierre Morel
2022-01-26T08:29:14Z

On 1/25/22 15:47, Matthew Rosato wrote:
> On 1/25/22 8:29 AM, Pierre Morel wrote:
>>
>>
>> On 1/14/22 21:31, 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 PCI I/O Address
>>> Translation assistance.
>>>
>>> Signed-off-by: Matthew Rosato <mjrosato@linux.ibm.com>
>>> ---
>>>   arch/s390/include/asm/kvm_pci.h |  15 ++++
>>>   arch/s390/include/asm/pci_dma.h |   2 +
>>>   arch/s390/kvm/pci.c             | 139 ++++++++++++++++++++++++++++++++
>>>   arch/s390/kvm/pci.h             |   2 +
>>>   4 files changed, 158 insertions(+)
>>>
>>> diff --git a/arch/s390/include/asm/kvm_pci.h
>>> b/arch/s390/include/asm/kvm_pci.h
>>> index 01fe14fffd7a..770849f13a70 100644
>>> --- a/arch/s390/include/asm/kvm_pci.h
>>> +++ b/arch/s390/include/asm/kvm_pci.h
>>> @@ -16,11 +16,21 @@
>>>   #include <linux/kvm_host.h>
>>>   #include <linux/kvm.h>
>>>   #include <linux/pci.h>
>>> +#include <linux/mutex.h>
>>>   #include <asm/pci_insn.h>
>>> +#include <asm/pci_dma.h>
>>> +
>>> +struct kvm_zdev_ioat {
>>> +    unsigned long *head[ZPCI_TABLE_PAGES];
>>> +    unsigned long **seg;
>>> +    unsigned long ***pt;
>>> +    struct mutex lock;
>>
>> Can we please rename the mutex ioat_lock to have a unique name easy to
>> follow for maintenance.
>> Can you please add a description about when the lock should be used?
>>
>
> OK.  The lock is meant to protect the contents of kvm_zdev_ioat -- I'll
> think of something to describe it.
>
>>> +};
>>>   struct kvm_zdev {
>>>       struct zpci_dev *zdev;
>>>       struct kvm *kvm;
>>> +    struct kvm_zdev_ioat ioat;
>>>       struct zpci_fib fib;
>>>   };
>>> @@ -33,6 +43,11 @@ int kvm_s390_pci_aif_enable(struct zpci_dev *zdev,
>>> struct zpci_fib *fib,
>>>                   bool assist);
>>>   int kvm_s390_pci_aif_disable(struct zpci_dev *zdev);
>>> +int kvm_s390_pci_ioat_probe(struct zpci_dev *zdev);
>>> +int kvm_s390_pci_ioat_enable(struct zpci_dev *zdev, u64 iota);
>>> +int kvm_s390_pci_ioat_disable(struct zpci_dev *zdev);
>>> +u8 kvm_s390_pci_get_dtsm(struct zpci_dev *zdev);
>>> +
>>>   int kvm_s390_pci_interp_probe(struct zpci_dev *zdev);
>>>   int kvm_s390_pci_interp_enable(struct zpci_dev *zdev);
>>>   int kvm_s390_pci_interp_disable(struct zpci_dev *zdev);
>>> diff --git a/arch/s390/include/asm/pci_dma.h
>>> b/arch/s390/include/asm/pci_dma.h
>>> index 91e63426bdc5..69e616d0712c 100644
>>> --- a/arch/s390/include/asm/pci_dma.h
>>> +++ b/arch/s390/include/asm/pci_dma.h
>>> @@ -50,6 +50,8 @@ enum zpci_ioat_dtype {
>>>   #define ZPCI_TABLE_ALIGN        ZPCI_TABLE_SIZE
>>>   #define ZPCI_TABLE_ENTRY_SIZE        (sizeof(unsigned long))
>>>   #define ZPCI_TABLE_ENTRIES        (ZPCI_TABLE_SIZE /
>>> ZPCI_TABLE_ENTRY_SIZE)
>>> +#define ZPCI_TABLE_PAGES        (ZPCI_TABLE_SIZE >> PAGE_SHIFT)
>>> +#define ZPCI_TABLE_ENTRIES_PAGES    (ZPCI_TABLE_ENTRIES *
>>> ZPCI_TABLE_PAGES)
>>>   #define ZPCI_TABLE_BITS            11
>>>   #define ZPCI_PT_BITS            8
>>> diff --git a/arch/s390/kvm/pci.c b/arch/s390/kvm/pci.c
>>> index 7ed9abc476b6..39c13c25a700 100644
>>> --- a/arch/s390/kvm/pci.c
>>> +++ b/arch/s390/kvm/pci.c
>>> @@ -13,12 +13,15 @@
>>>   #include <asm/pci.h>
>>>   #include <asm/pci_insn.h>
>>>   #include <asm/pci_io.h>
>>> +#include <asm/pci_dma.h>
>>>   #include <asm/sclp.h>
>>>   #include "pci.h"
>>>   #include "kvm-s390.h"
>>>   struct zpci_aift *aift;
>>> +#define shadow_ioat_init zdev->kzdev->ioat.head[0]
>>> +
>>>   static inline int __set_irq_noiib(u16 ctl, u8 isc)
>>>   {
>>>       union zpci_sic_iib iib = {{0}};
>>> @@ -344,6 +347,135 @@ int kvm_s390_pci_aif_disable(struct zpci_dev
>>> *zdev)
>>>   }
>>>   EXPORT_SYMBOL_GPL(kvm_s390_pci_aif_disable);
>>> +int kvm_s390_pci_ioat_probe(struct zpci_dev *zdev)
>>> +{
>>> +    /* Must have a KVM association registered */
>>
>> may be add something like : "The ioat structure is embeded in kzdev"
>>
>>> +    if (!zdev->kzdev || !zdev->kzdev->kvm)
>>
>> Why do we need to check for kvm ?
>> Having kzdev is already tested by the unique caller.
>>
>
> We probably don't need to check for the kzdev because the caller already
> did this, agreed there.
>
> But as for checking the kvm association, Alex asked for this in a
> comment to v1 (comment was against one of the vfio patches that call
> these routines) -- The reason being the probe comes from a userspace
> request and can be against any vfio-pci(-zdev) device at any time, and
> there's no point in proceeding if this device is not associated with a
> KVM guest -- It's possible for the KVM notifier to also pass a null KVM
> address -- so I think it's better to just be sure here.  In a
> well-behaved environment we would never see this (so, another case for
> an s390dbf entry)

I thought the check could be done even if the userspace is not
associated with KVM. But of course OK if Alex asked I would have missed
some point.

--
Pierre Morel
IBM Lab Boeblingen