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

[Pierre Morel]

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@xxxxxxxxxxxxx>
> > > ---
> > >   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