[PATCH kernel v7 10/10] KVM: PPC: VFIO: Add in-kernel acceleration for VFIO

[David Gibson]

On Thu, Mar 09, 2017 at 10:55:48PM +1100, Alexey Kardashevskiy wrote:
> 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.

Not really.  The H_HARDWARE tells the guest that something went
wrong.  The WARN_ON tells the _host_ that something went horribly
wrong.

> > [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.

I don't entirely follow your explanation, but ok.  Please correct this
in the respin.

> 
> > 
> >> +
> >> +	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.

Ok, can you add a comment about this say
  /* real mode xchg can fail if struct page crosses a page boundary */

.. and, if that's the case, shouldn't it be H_TOO_HARD not H_HARDWARE,
since the virtual mode one will be able to handle this?

> 
> 
> > 
> >> +
> >> +	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(&param, (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);
> > 
> 
> 




-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson
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