[PATCH kernel v7 10/10] KVM: PPC: VFIO: Add in-kernel acceleration for VFIO
Alexey Kardashevskiy
aik at ozlabs.ru
Thu Mar 9 22:55:48 AEDT 2017
On 09/03/17 17:47, David Gibson wrote:
> On Wed, Mar 08, 2017 at 02:00:11PM +1100, Alexey Kardashevskiy wrote:
>> This allows the host kernel to handle H_PUT_TCE, H_PUT_TCE_INDIRECT
>> and H_STUFF_TCE requests targeted an IOMMU TCE table used for VFIO
>> without passing them to user space which saves time on switching
>> to user space and back.
>>
>> This adds H_PUT_TCE/H_PUT_TCE_INDIRECT/H_STUFF_TCE handlers to KVM.
>> KVM tries to handle a TCE request in the real mode, if failed
>> it passes the request to the virtual mode to complete the operation.
>> If it a virtual mode handler fails, the request is passed to
>> the user space; this is not expected to happen though.
>>
>> To avoid dealing with page use counters (which is tricky in real mode),
>> this only accelerates SPAPR TCE IOMMU v2 clients which are required
>> to pre-register the userspace memory. The very first TCE request will
>> be handled in the VFIO SPAPR TCE driver anyway as the userspace view
>> of the TCE table (iommu_table::it_userspace) is not allocated till
>> the very first mapping happens and we cannot call vmalloc in real mode.
>>
>> If we fail to update a hardware IOMMU table unexpected reason, we just
>> clear it and move on as there is nothing really we can do about it -
>> for example, if we hot plug a VFIO device to a guest, existing TCE tables
>> will be mirrored automatically to the hardware and there is no interface
>> to report to the guest about possible failures.
>>
>> This adds new attribute - KVM_DEV_VFIO_GROUP_SET_SPAPR_TCE - to
>> the VFIO KVM device. It takes a VFIO group fd and SPAPR TCE table fd
>> and associates a physical IOMMU table with the SPAPR TCE table (which
>> is a guest view of the hardware IOMMU table). The iommu_table object
>> is cached and referenced so we do not have to look up for it in real mode.
>>
>> This does not implement the UNSET counterpart as there is no use for it -
>> once the acceleration is enabled, the existing userspace won't
>> disable it unless a VFIO container is destroyed; this adds necessary
>> cleanup to the KVM_DEV_VFIO_GROUP_DEL handler.
>>
>> As this creates a descriptor per IOMMU table-LIOBN couple (called
>> kvmppc_spapr_tce_iommu_table), it is possible to have several
>> descriptors with the same iommu_table (hardware IOMMU table) attached
>> to the same LIOBN; we do not remove duplicates though as
>> iommu_table_ops::exchange not just update a TCE entry (which is
>> shared among IOMMU groups) but also invalidates the TCE cache
>> (one per IOMMU group).
>>
>> This advertises the new KVM_CAP_SPAPR_TCE_VFIO capability to the user
>> space.
>>
>> This finally makes use of vfio_external_user_iommu_id() which was
>> introduced quite some time ago and was considered for removal.
>>
>> Tests show that this patch increases transmission speed from 220MB/s
>> to 750..1020MB/s on 10Gb network (Chelsea CXGB3 10Gb ethernet card).
>>
>> Signed-off-by: Alexey Kardashevskiy <aik at ozlabs.ru>
>
> There are still a few oddities in the error paths.
>
> [snip]
>> +static long kvmppc_tce_iommu_unmap(struct kvm *kvm,
>> + struct iommu_table *tbl, unsigned long entry)
>> +{
>> + enum dma_data_direction dir = DMA_NONE;
>> + unsigned long hpa = 0;
>> + long ret;
>> +
>> + if (iommu_tce_xchg(tbl, entry, &hpa, &dir))
>> + return H_HARDWARE;
>
> IIR previous discussions properly, an xchg() failure should be a
> WARN_ON().
Well, it could, I'll add. It just feels sometime that having both WARN_ON
and H_HARDWARE is kind of redundant.
> [snip]
>> +static long kvmppc_rm_tce_iommu_mapped_dec(struct kvm *kvm,
>> + struct iommu_table *tbl, unsigned long entry)
>> +{
>> + struct mm_iommu_table_group_mem_t *mem = NULL;
>> + const unsigned long pgsize = 1ULL << tbl->it_page_shift;
>> + unsigned long *pua = IOMMU_TABLE_USERSPACE_ENTRY(tbl, entry);
>> +
>> + if (WARN_ON_ONCE_RM(!pua))
>> + return H_HARDWARE;
>> +
>> + pua = (void *) vmalloc_to_phys(pua);
>> + if (!pua)
>> + return H_TOO_HARD;
>
> Here a vmalloc translation failure is treated as an H_TOO_HARD..
Ah, here is an oddity, here should be WARN_ON + H_HARDWARE and the if(!pua)
check should not do WARN_ON and return H_TOO_HARD, I did not hit this
because the hardware is empty when VFIO starts using it so there is nothing
to unmap initial H_STUFF_TCE happens.
>
>> +
>> + mem = mm_iommu_lookup_rm(kvm->mm, *pua, pgsize);
>> + if (!mem)
>> + return H_TOO_HARD;
>> +
>> + mm_iommu_mapped_dec(mem);
>> +
>> + *pua = 0;
>> +
>> + return H_SUCCESS;
>> +}
>> +
>> +static long kvmppc_rm_tce_iommu_unmap(struct kvm *kvm,
>> + struct iommu_table *tbl, unsigned long entry)
>> +{
>> + enum dma_data_direction dir = DMA_NONE;
>> + unsigned long hpa = 0;
>> + long ret;
>> +
>> + if (iommu_tce_xchg_rm(tbl, entry, &hpa, &dir))
>> + return H_HARDWARE;
>
> Another xchg failure where I'd expect a WARN.
The realmode's iommu_tce_xchg_rm() does SetPageDirty() if
realmode_pfn_to_page() succeeded but realmode_pfn_to_page() may fail if the
requested page struct is split between 2 system pages in real addressspace
but not in virtual address space where page structs are mapped to
0xfxxx.xxxx.xxxx.xxxx.
>
>> +
>> + if (dir == DMA_NONE)
>> + return H_SUCCESS;
>> +
>> + ret = kvmppc_rm_tce_iommu_mapped_dec(kvm, tbl, entry);
>> + if (ret)
>> + iommu_tce_xchg_rm(tbl, entry, &hpa, &dir);
>> +
>> + return ret;
>> +}
>> +
>> +static long kvmppc_rm_tce_iommu_map(struct kvm *kvm, struct iommu_table *tbl,
>> + unsigned long entry, unsigned long ua,
>> + enum dma_data_direction dir)
>> +{
>> + long ret;
>> + unsigned long hpa = 0;
>> + unsigned long *pua = IOMMU_TABLE_USERSPACE_ENTRY(tbl, entry);
>> + struct mm_iommu_table_group_mem_t *mem;
>> +
>> + if (!pua)
>> + /* it_userspace allocation might be delayed */
>> + return H_TOO_HARD;
>> +
>> + mem = mm_iommu_lookup_rm(kvm->mm, ua, 1ULL << tbl->it_page_shift);
>> + if (!mem)
>> + return H_TOO_HARD;
>> +
>> + if (WARN_ON_ONCE_RM(mm_iommu_ua_to_hpa_rm(mem, ua, &hpa)))
>> + return H_HARDWARE;
>> +
>> + pua = (void *) vmalloc_to_phys(pua);
>> + if (WARN_ON_ONCE_RM(!pua))
>
> .. but here a more or less identical vmalloc translation failure is
> treated as a WARN. Is it TOO_HARD, or WARN?
This one is correct.
>
>> + return H_HARDWARE;
>> +
>> + if (WARN_ON_ONCE_RM(mm_iommu_mapped_inc(mem)))
>> + return H_CLOSED;
>> +
>> + ret = iommu_tce_xchg_rm(tbl, entry, &hpa, &dir);
>> + if (ret) {
>> + mm_iommu_mapped_dec(mem);
>> + return H_TOO_HARD;
>
> And another xchg failure that I'd expect to be a warn
Here it is the realmode's iommu_tce_xchg again.
>
>> + }
>> +
>> + if (dir != DMA_NONE)
>> + kvmppc_rm_tce_iommu_mapped_dec(kvm, tbl, entry);
>> +
>> + *pua = ua;
>> +
>> + return 0;
>> +}
>> +
>> long kvmppc_rm_h_put_tce(struct kvm_vcpu *vcpu, unsigned long liobn,
>> unsigned long ioba, unsigned long tce)
>> {
>> struct kvmppc_spapr_tce_table *stt;
>> long ret;
>> + struct kvmppc_spapr_tce_iommu_table *stit;
>> + unsigned long entry, ua = 0;
>> + enum dma_data_direction dir;
>>
>> /* udbg_printf("H_PUT_TCE(): liobn=0x%lx ioba=0x%lx, tce=0x%lx\n", */
>> /* liobn, ioba, tce); */
>> @@ -182,7 +304,32 @@ long kvmppc_rm_h_put_tce(struct kvm_vcpu *vcpu, unsigned long liobn,
>> if (ret != H_SUCCESS)
>> return ret;
>>
>> - kvmppc_tce_put(stt, ioba >> stt->page_shift, tce);
>> + dir = iommu_tce_direction(tce);
>> + if ((dir != DMA_NONE) && kvmppc_gpa_to_ua(vcpu->kvm,
>> + tce & ~(TCE_PCI_READ | TCE_PCI_WRITE), &ua, NULL))
>> + return H_PARAMETER;
>> +
>> + entry = ioba >> stt->page_shift;
>> +
>> + list_for_each_entry_lockless(stit, &stt->iommu_tables, next) {
>> + if (dir == DMA_NONE)
>> + ret = kvmppc_rm_tce_iommu_unmap(vcpu->kvm,
>> + stit->tbl, entry);
>> + else
>> + ret = kvmppc_rm_tce_iommu_map(vcpu->kvm,
>> + stit->tbl, entry, ua, dir);
>> +
>> + if (ret == H_SUCCESS)
>> + continue;
>> +
>> + if (ret == H_TOO_HARD)
>> + return ret;
>> +
>> + WARN_ON_ONCE_RM(1);
>> + kvmppc_rm_clear_tce(stit->tbl, entry);
>> + }
>> +
>> + kvmppc_tce_put(stt, entry, tce);
>>
>> return H_SUCCESS;
>> }
>> @@ -223,6 +370,7 @@ long kvmppc_rm_h_put_tce_indirect(struct kvm_vcpu *vcpu,
>> unsigned long tces, entry, ua = 0;
>> unsigned long *rmap = NULL;
>> bool prereg = false;
>> + struct kvmppc_spapr_tce_iommu_table *stit;
>>
>> stt = kvmppc_find_table(vcpu->kvm, liobn);
>> if (!stt)
>> @@ -293,6 +441,27 @@ long kvmppc_rm_h_put_tce_indirect(struct kvm_vcpu *vcpu,
>> if (ret != H_SUCCESS)
>> goto unlock_exit;
>>
>> + ua = 0;
>> + if (kvmppc_gpa_to_ua(vcpu->kvm,
>> + tce & ~(TCE_PCI_READ | TCE_PCI_WRITE),
>> + &ua, NULL))
>> + return H_PARAMETER;
>> +
>> + list_for_each_entry_lockless(stit, &stt->iommu_tables, next) {
>> + ret = kvmppc_rm_tce_iommu_map(vcpu->kvm,
>> + stit->tbl, entry + i, ua,
>> + iommu_tce_direction(tce));
>> +
>> + if (ret == H_SUCCESS)
>> + continue;
>> +
>> + if (ret == H_TOO_HARD)
>> + goto unlock_exit;
>> +
>> + WARN_ON_ONCE_RM(1);
>> + kvmppc_rm_clear_tce(stit->tbl, entry);
>> + }
>> +
>> kvmppc_tce_put(stt, entry + i, tce);
>> }
>>
>> @@ -309,6 +478,7 @@ long kvmppc_rm_h_stuff_tce(struct kvm_vcpu *vcpu,
>> {
>> struct kvmppc_spapr_tce_table *stt;
>> long i, ret;
>> + struct kvmppc_spapr_tce_iommu_table *stit;
>>
>> stt = kvmppc_find_table(vcpu->kvm, liobn);
>> if (!stt)
>> @@ -322,6 +492,24 @@ long kvmppc_rm_h_stuff_tce(struct kvm_vcpu *vcpu,
>> if (tce_value & (TCE_PCI_WRITE | TCE_PCI_READ))
>> return H_PARAMETER;
>>
>> + list_for_each_entry_lockless(stit, &stt->iommu_tables, next) {
>> + unsigned long entry = ioba >> stit->tbl->it_page_shift;
>> +
>> + for (i = 0; i < npages; ++i) {
>> + ret = kvmppc_rm_tce_iommu_unmap(vcpu->kvm,
>> + stit->tbl, entry + i);
>> +
>> + if (ret == H_SUCCESS)
>> + continue;
>> +
>> + if (ret == H_TOO_HARD)
>> + return ret;
>> +
>> + WARN_ON_ONCE_RM(1);
>> + kvmppc_rm_clear_tce(stit->tbl, entry);
>> + }
>> + }
>> +
>> for (i = 0; i < npages; ++i, ioba += (1ULL << stt->page_shift))
>> kvmppc_tce_put(stt, ioba >> stt->page_shift, tce_value);
>>
>> diff --git a/arch/powerpc/kvm/powerpc.c b/arch/powerpc/kvm/powerpc.c
>> index 95c91a9de351..62bdd6c48107 100644
>> --- a/arch/powerpc/kvm/powerpc.c
>> +++ b/arch/powerpc/kvm/powerpc.c
>> @@ -538,6 +538,8 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
>> #ifdef CONFIG_PPC_BOOK3S_64
>> case KVM_CAP_SPAPR_TCE:
>> case KVM_CAP_SPAPR_TCE_64:
>> + /* fallthrough */
>> + case KVM_CAP_SPAPR_TCE_VFIO:
>> case KVM_CAP_PPC_RTAS:
>> case KVM_CAP_PPC_FIXUP_HCALL:
>> case KVM_CAP_PPC_ENABLE_HCALL:
>> diff --git a/virt/kvm/vfio.c b/virt/kvm/vfio.c
>> index d32f239eb471..2b7dc22265fe 100644
>> --- a/virt/kvm/vfio.c
>> +++ b/virt/kvm/vfio.c
>> @@ -20,6 +20,10 @@
>> #include <linux/vfio.h>
>> #include "vfio.h"
>>
>> +#ifdef CONFIG_SPAPR_TCE_IOMMU
>> +#include <asm/kvm_ppc.h>
>> +#endif
>> +
>> struct kvm_vfio_group {
>> struct list_head node;
>> struct vfio_group *vfio_group;
>> @@ -211,6 +215,9 @@ static int kvm_vfio_set_group(struct kvm_device *dev, long attr, u64 arg)
>>
>> mutex_unlock(&kv->lock);
>>
>> +#ifdef CONFIG_SPAPR_TCE_IOMMU
>> + kvm_spapr_tce_release_iommu_group(dev->kvm, vfio_group);
>> +#endif
>> kvm_vfio_group_set_kvm(vfio_group, NULL);
>>
>> kvm_vfio_group_put_external_user(vfio_group);
>> @@ -218,6 +225,53 @@ static int kvm_vfio_set_group(struct kvm_device *dev, long attr, u64 arg)
>> kvm_vfio_update_coherency(dev);
>>
>> return ret;
>> +
>> +#ifdef CONFIG_SPAPR_TCE_IOMMU
>> + case KVM_DEV_VFIO_GROUP_SET_SPAPR_TCE: {
>> + struct kvm_vfio_spapr_tce param;
>> + unsigned long minsz;
>> + struct kvm_vfio *kv = dev->private;
>> + struct vfio_group *vfio_group;
>> + struct kvm_vfio_group *kvg;
>> + struct fd f;
>> +
>> + minsz = offsetofend(struct kvm_vfio_spapr_tce, tablefd);
>> +
>> + if (copy_from_user(¶m, (void __user *)arg, minsz))
>> + return -EFAULT;
>> +
>> + if (param.argsz < minsz || param.flags)
>> + return -EINVAL;
>> +
>> + f = fdget(param.groupfd);
>> + if (!f.file)
>> + return -EBADF;
>> +
>> + vfio_group = kvm_vfio_group_get_external_user(f.file);
>> + fdput(f);
>> +
>> + if (IS_ERR(vfio_group))
>> + return PTR_ERR(vfio_group);
>> +
>> + ret = -ENOENT;
>> +
>> + mutex_lock(&kv->lock);
>> +
>> + list_for_each_entry(kvg, &kv->group_list, node) {
>> + if (kvg->vfio_group != vfio_group)
>> + continue;
>> +
>> + ret = kvm_spapr_tce_attach_iommu_group(dev->kvm,
>> + param.tablefd, vfio_group);
>> +
>> + break;
>> + }
>> +
>> + mutex_unlock(&kv->lock);
>> +
>> + return ret;
>> + }
>> +#endif /* CONFIG_SPAPR_TCE_IOMMU */
>> }
>>
>> return -ENXIO;
>> @@ -242,6 +296,9 @@ static int kvm_vfio_has_attr(struct kvm_device *dev,
>> switch (attr->attr) {
>> case KVM_DEV_VFIO_GROUP_ADD:
>> case KVM_DEV_VFIO_GROUP_DEL:
>> +#ifdef CONFIG_SPAPR_TCE_IOMMU
>> + case KVM_DEV_VFIO_GROUP_SET_SPAPR_TCE:
>> +#endif
>> return 0;
>> }
>>
>> @@ -257,6 +314,9 @@ static void kvm_vfio_destroy(struct kvm_device *dev)
>> struct kvm_vfio_group *kvg, *tmp;
>>
>> list_for_each_entry_safe(kvg, tmp, &kv->group_list, node) {
>> +#ifdef CONFIG_SPAPR_TCE_IOMMU
>> + kvm_spapr_tce_release_iommu_group(dev->kvm, kvg->vfio_group);
>> +#endif
>> kvm_vfio_group_set_kvm(kvg->vfio_group, NULL);
>> kvm_vfio_group_put_external_user(kvg->vfio_group);
>> list_del(&kvg->node);
>
--
Alexey
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