Re: [PATCH 22/32] KVM: s390: pci: provide routines for enabling/disabling IOAT assist

[Matthew Rosato <mjrosato@linux.ibm.com>]

On 12/14/21 12:46 PM, Pierre Morel wrote:
> 
> 
> On 12/7/21 21:57, 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             | 133 ++++++++++++++++++++++++++++++++
>>   arch/s390/kvm/pci.h             |   2 +
>>   4 files changed, 152 insertions(+)
>>
>> diff --git a/arch/s390/include/asm/kvm_pci.h 
>> b/arch/s390/include/asm/kvm_pci.h
>> index 54a0afdbe7d0..254275399f21 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;
>> +};
>>   struct kvm_zdev {
>>       struct zpci_dev *zdev;
>>       struct kvm *kvm;
>> +    struct kvm_zdev_ioat ioat;
>>       struct zpci_fib fib;
>>   };
>> @@ -33,6 +43,11 @@ extern int kvm_s390_pci_aif_enable(struct zpci_dev 
>> *zdev, struct zpci_fib *fib,
>>                      bool assist);
>>   extern int kvm_s390_pci_aif_disable(struct zpci_dev *zdev);
>> +extern int kvm_s390_pci_ioat_probe(struct zpci_dev *zdev);
>> +extern int kvm_s390_pci_ioat_enable(struct zpci_dev *zdev, u64 iota);
>> +extern int kvm_s390_pci_ioat_disable(struct zpci_dev *zdev);
>> +extern u8 kvm_s390_pci_get_dtsm(struct zpci_dev *zdev);
>> +
>>   extern int kvm_s390_pci_interp_probe(struct zpci_dev *zdev);
>>   extern int kvm_s390_pci_interp_enable(struct zpci_dev *zdev);
>>   extern 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 3b8e89d4578a..e1d3c1d3fc8a 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 3a29398dd53b..a1c0c0881332 100644
>> --- a/arch/s390/kvm/pci.c
>> +++ b/arch/s390/kvm/pci.c
>> @@ -12,6 +12,7 @@
>>   #include <asm/kvm_pci.h>
>>   #include <asm/pci.h>
>>   #include <asm/pci_insn.h>
>> +#include <asm/pci_dma.h>
>>   #include <asm/sclp.h>
>>   #include "pci.h"
>>   #include "kvm-s390.h"
>> @@ -315,6 +316,131 @@ 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)
>> +{
>> +    return 0;
>> +}
>> +EXPORT_SYMBOL_GPL(kvm_s390_pci_ioat_probe);
>> +
>> +int kvm_s390_pci_ioat_enable(struct zpci_dev *zdev, u64 iota)
>> +{
>> +    gpa_t gpa = (gpa_t)(iota & ZPCI_RTE_ADDR_MASK);
>> +    struct kvm_zdev_ioat *ioat;
>> +    struct page *page;
>> +    struct kvm *kvm;
>> +    unsigned int idx;
>> +    void *iaddr;
>> +    int i, rc = 0;
>> +
>> +    if (!zdev->kzdev || !zdev->kzdev->kvm || zdev->kzdev->ioat.head[0])
>> +        return -EINVAL;
> 
> The only caller already checked zdev->kzdev.

I tend to get overzealous with these checks..

> Could we use a macro to replace zdev->kzdev->ioat.head[0] ?
> like
> #define shadow_pgtbl_initialized zdev->kzdev->ioat.head[0] >
> Would be clearer for me.

Sure

> 
>> +
>> +    /* Ensure supported type specified */
>> +    if ((iota & ZPCI_IOTA_RTTO_FLAG) != ZPCI_IOTA_RTTO_FLAG)
>> +        return -EINVAL;
>> +
>> +    kvm = zdev->kzdev->kvm;
>> +    ioat = &zdev->kzdev->ioat;
>> +    mutex_lock(&ioat->lock);
>> +    idx = srcu_read_lock(&kvm->srcu);
>> +    for (i = 0; i < ZPCI_TABLE_PAGES; i++) {
>> +        page = gfn_to_page(kvm, gpa_to_gfn(gpa));

In relation to your question below about where things are being pinned...

Here the call to gfn_to_page does the pin (this call eventually drives 
hva_to_pfn for pinning)

>> +        if (is_error_page(page)) {
>> +            srcu_read_unlock(&kvm->srcu, idx);
>> +            rc = -EIO;
>> +            goto out;
>> +        }
>> +        iaddr = page_to_virt(page) + (gpa & ~PAGE_MASK);
>> +        ioat->head[i] = (unsigned long *)iaddr;

^^ here we store what was pinned above in ioat->head[] and can use it 
later for unpinning.

But looking again now I think for the is_error_page() case above here I 
should also be going to unpin: to cleanup in case we were somewhere in 
the middle of the loop and so have some pages pinned already.

>> +        gpa += PAGE_SIZE;
>> +    }
>> +    srcu_read_unlock(&kvm->srcu, idx);
>> +
>> +    zdev->kzdev->ioat.seg = kcalloc(ZPCI_TABLE_ENTRIES_PAGES,
>> +                    sizeof(unsigned long *), GFP_KERNEL);
>> +    if (!zdev->kzdev->ioat.seg)
>> +        goto unpin;
>> +    zdev->kzdev->ioat.pt = kcalloc(ZPCI_TABLE_ENTRIES,
>> +                       sizeof(unsigned long **), GFP_KERNEL);
>> +    if (!zdev->kzdev->ioat.pt)
>> +        goto free_seg;
>> +
>> +out:
>> +    mutex_unlock(&ioat->lock);
>> +    return rc;
>> +
>> +free_seg:
>> +    kfree(zdev->kzdev->ioat.seg);
>> +unpin:
>> +    for (i = 0; i < ZPCI_TABLE_PAGES; i++) {
>> +        kvm_release_pfn_dirty((u64)ioat->head[i] >> PAGE_SHIFT);
> 
> I did not find when the pages are pinned.

See above.

> 
>> +        ioat->head[i] = 0;
>> +    }
>> +    mutex_unlock(&ioat->lock);
>> +    return -ENOMEM;
>> +}
>> +EXPORT_SYMBOL_GPL(kvm_s390_pci_ioat_enable);
>> +
> 
> ...snip...
>>
>