Re: [PATCH kernel v4 10/10] KVM: PPC: VFIO: Add in-kernel acceleration for VFIO

Alexey Kardashevskiy
2017-02-10T02:50:31Z

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On 09/02/17 17:41, David Gibson wrote:
> On Tue, Feb 07, 2017 at 06:17:11PM +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.
>>
>> 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@ozlabs.ru>
>> ---
>> Changes:
>> v4:
>> * added note to the commit log about allowing multiple updates of
>> the same IOMMU table;
>> * instead of checking for if any memory was preregistered, this
>> returns H_TOO_HARD if a specific page was not;
>> * fixed comments from v3 about error handling in many places;
>> * simplified TCE handlers and merged IOMMU parts inline - for example,
>> there used to be kvmppc_h_put_tce_iommu(), now it is merged into
>> kvmppc_h_put_tce(); this allows to check IOBA boundaries against
>> the first attached table only (makes the code simpler);
>>
>> v3:
>> * simplified not to use VFIO group notifiers
>> * reworked cleanup, should be cleaner/simpler now
>>
>> v2:
>> * reworked to use new VFIO notifiers
>> * now same iommu_table may appear in the list several times, to be fixed later
>> ---
>>
>> This has separate copies of handlers for real and virtual modes as
>> in fact H_PUT_TCE and H_STUFF_TCE could share a lot (common helpers
>> would take a "realmode" flag) but H_PUT_TCE_INDIRECT uses get_user()
>> in virtual mode and direct access in real mode and having a common
>> helper for it would make things uglier imho.
>>
>>
>> ---
>> Documentation/virtual/kvm/devices/vfio.txt | 22 +-
>> arch/powerpc/include/asm/kvm_host.h | 8 +
>> arch/powerpc/include/asm/kvm_ppc.h | 4 +
>> include/uapi/linux/kvm.h | 8 +
>> arch/powerpc/kvm/book3s_64_vio.c | 319 ++++++++++++++++++++++++++++-
>> arch/powerpc/kvm/book3s_64_vio_hv.c | 172 +++++++++++++++-
>> arch/powerpc/kvm/powerpc.c | 2 +
>> virt/kvm/vfio.c | 60 ++++++
>> 8 files changed, 590 insertions(+), 5 deletions(-)
>>
>> diff --git a/Documentation/virtual/kvm/devices/vfio.txt b/Documentation/virtual/kvm/devices/vfio.txt
>> index ef51740c67ca..f95d867168ea 100644
>> --- a/Documentation/virtual/kvm/devices/vfio.txt
>> +++ b/Documentation/virtual/kvm/devices/vfio.txt
>> @@ -16,7 +16,25 @@ Groups:
>>
>> KVM_DEV_VFIO_GROUP attributes:
>> KVM_DEV_VFIO_GROUP_ADD: Add a VFIO group to VFIO-KVM device tracking
>> + kvm_device_attr.addr points to an int32_t file descriptor
>> + for the VFIO group.
>> KVM_DEV_VFIO_GROUP_DEL: Remove a VFIO group from VFIO-KVM device tracking
>> + kvm_device_attr.addr points to an int32_t file descriptor
>> + for the VFIO group.
>> + KVM_DEV_VFIO_GROUP_SET_SPAPR_TCE: attaches a guest visible TCE table
>> + allocated by sPAPR KVM.
>> + kvm_device_attr.addr points to a struct:
>>
>> -For each, kvm_device_attr.addr points to an int32_t file descriptor
>> -for the VFIO group.
>> + struct kvm_vfio_spapr_tce {
>> + __u32 argsz;
>> + __u32 flags;
>> + __s32 groupfd;
>> + __s32 tablefd;
>> + };
>> +
>> + where
>> + @argsz is the size of kvm_vfio_spapr_tce_liobn;
>> + @flags are not supported now, must be zero;
>> + @groupfd is a file descriptor for a VFIO group;
>> + @tablefd is a file descriptor for a TCE table allocated via
>> + KVM_CREATE_SPAPR_TCE.
>> diff --git a/arch/powerpc/include/asm/kvm_host.h b/arch/powerpc/include/asm/kvm_host.h
>> index e59b172666cd..a827006941f8 100644
>> --- a/arch/powerpc/include/asm/kvm_host.h
>> +++ b/arch/powerpc/include/asm/kvm_host.h
>> @@ -191,6 +191,13 @@ struct kvmppc_pginfo {
>> atomic_t refcnt;
>> };
>>
>> +struct kvmppc_spapr_tce_iommu_table {
>> + struct rcu_head rcu;
>> + struct list_head next;
>> + struct vfio_group *group;
>> + struct iommu_table *tbl;
>> +};
>> +
>> struct kvmppc_spapr_tce_table {
>> struct list_head list;
>> struct kvm *kvm;
>> @@ -199,6 +206,7 @@ struct kvmppc_spapr_tce_table {
>> u32 page_shift;
>> u64 offset; /* in pages */
>> u64 size; /* window size in pages */
>> + struct list_head iommu_tables;
>> struct page *pages[0];
>> };
>>
>> diff --git a/arch/powerpc/include/asm/kvm_ppc.h b/arch/powerpc/include/asm/kvm_ppc.h
>> index 37bc9e7e90ba..da1410bd6b36 100644
>> --- a/arch/powerpc/include/asm/kvm_ppc.h
>> +++ b/arch/powerpc/include/asm/kvm_ppc.h
>> @@ -163,6 +163,10 @@ extern long kvmppc_prepare_vrma(struct kvm *kvm,
>> extern void kvmppc_map_vrma(struct kvm_vcpu *vcpu,
>> struct kvm_memory_slot *memslot, unsigned long porder);
>> extern int kvmppc_pseries_do_hcall(struct kvm_vcpu *vcpu);
>> +extern long kvm_spapr_tce_attach_iommu_group(struct kvm *kvm, int tablefd,
>> + struct vfio_group *group);
>> +extern void kvm_spapr_tce_release_iommu_group(struct kvm *kvm,
>> + struct vfio_group *group);
>>
>> extern long kvm_vm_ioctl_create_spapr_tce(struct kvm *kvm,
>> struct kvm_create_spapr_tce_64 *args);
>> diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
>> index a2c9bb5a0ead..cdfa01169bd2 100644
>> --- a/include/uapi/linux/kvm.h
>> +++ b/include/uapi/linux/kvm.h
>> @@ -1076,6 +1076,7 @@ struct kvm_device_attr {
>> #define KVM_DEV_VFIO_GROUP 1
>> #define KVM_DEV_VFIO_GROUP_ADD 1
>> #define KVM_DEV_VFIO_GROUP_DEL 2
>> +#define KVM_DEV_VFIO_GROUP_SET_SPAPR_TCE 3
>>
>> enum kvm_device_type {
>> KVM_DEV_TYPE_FSL_MPIC_20 = 1,
>> @@ -1097,6 +1098,13 @@ enum kvm_device_type {
>> KVM_DEV_TYPE_MAX,
>> };
>>
>> +struct kvm_vfio_spapr_tce {
>> + __u32 argsz;
>> + __u32 flags;
>> + __s32 groupfd;
>> + __s32 tablefd;
>> +};
>> +
>> /*
>> * ioctls for VM fds
>> */
>> diff --git a/arch/powerpc/kvm/book3s_64_vio.c b/arch/powerpc/kvm/book3s_64_vio.c
>> index 9a7b7fca5e84..cb0469151e35 100644
>> --- a/arch/powerpc/kvm/book3s_64_vio.c
>> +++ b/arch/powerpc/kvm/book3s_64_vio.c
>> @@ -27,6 +27,10 @@
>> #include <linux/hugetlb.h>
>> #include <linux/list.h>
>> #include <linux/anon_inodes.h>
>> +#include <linux/iommu.h>
>> +#include <linux/file.h>
>> +#include <linux/vfio.h>
>> +#include <linux/module.h>
>>
>> #include <asm/tlbflush.h>
>> #include <asm/kvm_ppc.h>
>> @@ -39,6 +43,36 @@
>> #include <asm/udbg.h>
>> #include <asm/iommu.h>
>> #include <asm/tce.h>
>> +#include <asm/mmu_context.h>
>> +
>> +static void kvm_vfio_group_put_external_user(struct vfio_group *vfio_group)
>> +{
>> + void (*fn)(struct vfio_group *);
>> +
>> + fn = symbol_get(vfio_group_put_external_user);
>> + if (WARN_ON(!fn))
>> + return;
>> +
>> + fn(vfio_group);
>> +
>> + symbol_put(vfio_group_put_external_user);
>> +}
>> +
>> +static int kvm_vfio_external_user_iommu_id(struct vfio_group *vfio_group)
>> +{
>> + int (*fn)(struct vfio_group *);
>> + int ret = -1;
>> +
>> + fn = symbol_get(vfio_external_user_iommu_id);
>> + if (!fn)
>> + return ret;
>> +
>> + ret = fn(vfio_group);
>> +
>> + symbol_put(vfio_external_user_iommu_id);
>> +
>> + return ret;
>> +}
>>
>> static unsigned long kvmppc_tce_pages(unsigned long iommu_pages)
>> {
>> @@ -90,6 +124,123 @@ static long kvmppc_account_memlimit(unsigned long stt_pages, bool inc)
>> return ret;
>> }
>>
>> +static void kvm_spapr_tce_iommu_table_free(struct rcu_head *head)
>> +{
>> + struct kvmppc_spapr_tce_iommu_table *stit = container_of(head,
>> + struct kvmppc_spapr_tce_iommu_table, rcu);
>> +
>> + iommu_table_put(stit->tbl);
>> + kvm_vfio_group_put_external_user(stit->group);
>> +
>> + kfree(stit);
>> +}
>> +
>> +static void kvm_spapr_tce_liobn_release_iommu_group(
>> + struct kvmppc_spapr_tce_table *stt,
>> + struct vfio_group *group)
>> +{
>> + struct kvmppc_spapr_tce_iommu_table *stit, *tmp;
>> +
>> + list_for_each_entry_safe(stit, tmp, &stt->iommu_tables, next) {
>> + if (group && (stit->group != group))
>> + continue;
>> +
>> + list_del_rcu(&stit->next);
>> +
>> + call_rcu(&stit->rcu, kvm_spapr_tce_iommu_table_free);
>> + }
>> +}
>> +
>> +extern void kvm_spapr_tce_release_iommu_group(struct kvm *kvm,
>> + struct vfio_group *group)
>> +{
>> + struct kvmppc_spapr_tce_table *stt;
>> +
>> + list_for_each_entry_rcu(stt, &kvm->arch.spapr_tce_tables, list)
>> + kvm_spapr_tce_liobn_release_iommu_group(stt, group);
>> +}
>> +
>> +extern long kvm_spapr_tce_attach_iommu_group(struct kvm *kvm, int tablefd,
>> + struct vfio_group *group)
>> +{
>> + struct kvmppc_spapr_tce_table *stt = NULL;
>> + bool found = false;
>> + struct iommu_table *tbl = NULL;
>> + struct iommu_table_group *table_group;
>> + long i, ret = 0;
>> + struct kvmppc_spapr_tce_iommu_table *stit;
>> + struct fd f;
>> + int group_id;
>> + struct iommu_group *grp;
>> +
>> + group_id = kvm_vfio_external_user_iommu_id(group);
>> + grp = iommu_group_get_by_id(group_id);
>> + if (!grp)
>> + return -EFAULT;
>
> EFAULT doesn't look right, that's usually means userspace has give us
> a bad address. What does failure to look up the iommu group by id
> mean here?

iommu_group_get_by_id() can fail -
1. if "something went very wrong" - as group ids are allocated when devices
are discovered so they are pretty static;
2. there is some racy sriov disable or host pci hotunplug;
3. kvm_vfio_external_user_iommu_id() returned invalid group id which means
that a device was unbound from the vfio-pci driver but the caller holds a
reference to vfio_group so this should not happen.

>
>> +
>> + f = fdget(tablefd);
>> + if (!f.file) {
>> + ret = -EBADF;
>> + goto put_exit;
>> + }
>> +
>> + list_for_each_entry_rcu(stt, &kvm->arch.spapr_tce_tables, list) {
>> + if (stt == f.file->private_data) {
>> + found = true;
>> + break;
>> + }
>> + }
>> +
>> + fdput(f);
>> +
>> + if (!found) {
>> + ret = -ENODEV;
>
> ENODEV doesn't look right either. That generally means you're trying
> to use a device or facility that doesn't exist. This case just means
> you've passed a file handle that either isn't a TCE table at all, or
> os one associated with a different VM. -EINVAL, I guess, overloaded
> as it is.

Ok.

>
>> + goto put_exit;
>
> Don't you need to put the table fd as well as the iommu group which
> you put in that exit path?

It is put few lines above.

>> + }
>> +
>> + table_group = iommu_group_get_iommudata(grp);
>> + if (WARN_ON(!table_group)) {
>> + ret = -EFAULT;
>> + goto put_exit;
>
> Again don't you need to put the table fd as well.

It is put few lines above, I do not keep it open longer than needed.

>
>> + }
>> +
>> + for (i = 0; i < IOMMU_TABLE_GROUP_MAX_TABLES; ++i) {
>> + struct iommu_table *tbltmp = table_group->tables[i];
>> +
>> + if (!tbltmp)
>> + continue;
>> +
>> + /*
>> + * Make sure hardware table parameters are exactly the same;
>> + * this is used in the TCE handlers where boundary checks
>> + * use only the first attached table.
>> + */
>> + if ((tbltmp->it_page_shift == stt->page_shift) &&
>> + (tbltmp->it_offset == stt->offset) &&
>> + (tbltmp->it_size == stt->size)) {
>> + tbl = tbltmp;
>> + break;
>> + }
>> + }
>> + if (!tbl) {
>> + ret = -ENODEV;
>
> Again, ENODEV doesn't seem right. Here the problem is that the host
> hardware constraints don't match the guest hardware constraints.
> Hmm. EIO? ENOSPC?

Neither is very appealing to me... EINVAL?
When I use "ENODEV", I am thinking of "there is no device with
expected/requested characteristics" but this is probably wrong.

>
>> + goto put_exit;
>> + }
>> +
>> + iommu_table_get(tbl);
>> +
>> + stit = kzalloc(sizeof(*stit), GFP_KERNEL);
>> + stit->tbl = tbl;
>> + stit->group = group;
>> +
>> + list_add_rcu(&stit->next, &stt->iommu_tables);
>
> So if you add the same group to the same liobn multiple times, you'll
> get multiple identical entries in this list.
>
> I guess that's mostly harmless... although.. does it allow the user to
> force the allocation of arbitrary amounts of kernel memory in that
> list?

Oh. No, I'll add a check to avoid duplicates, they do not make sense here.

>
>> +put_exit:
>> + iommu_group_put(grp);
>> +
>> + return ret;
>> +}
>> +
>> static void release_spapr_tce_table(struct rcu_head *head)
>> {
>> struct kvmppc_spapr_tce_table *stt = container_of(head,
>> @@ -132,6 +283,8 @@ static int kvm_spapr_tce_release(struct inode *inode, struct file *filp)
>>
>> list_del_rcu(&stt->list);
>>
>> + kvm_spapr_tce_liobn_release_iommu_group(stt, NULL /* release all */);
>> +
>> kvm_put_kvm(stt->kvm);
>>
>> kvmppc_account_memlimit(
>> @@ -181,6 +334,7 @@ long kvm_vm_ioctl_create_spapr_tce(struct kvm *kvm,
>> stt->offset = args->offset;
>> stt->size = size;
>> stt->kvm = kvm;
>> + INIT_LIST_HEAD_RCU(&stt->iommu_tables);
>>
>> for (i = 0; i < npages; i++) {
>> stt->pages[i] = alloc_page(GFP_KERNEL | __GFP_ZERO);
>> @@ -209,11 +363,94 @@ long kvm_vm_ioctl_create_spapr_tce(struct kvm *kvm,
>> return ret;
>> }
>>
>> +static long kvmppc_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 (!pua)
>> + return H_HARDWARE;
>
> What could trigger this error? Should it be a WARN_ON?

Nothing should so yes, it can be WARN_ON.

>
>> + mem = mm_iommu_lookup(kvm->mm, *pua, pgsize);
>> + if (!mem)
>> + return H_TOO_HARD;
>> +
>> + mm_iommu_mapped_dec(mem);
>> +
>> + *pua = 0;
>> +
>> + return H_SUCCESS;
>> +}
>> +
>> +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;
>> +
>> + if (dir == DMA_NONE)
>> + return H_SUCCESS;
>> +
>> + ret = kvmppc_tce_iommu_mapped_dec(kvm, tbl, entry);
>> + if (ret != H_SUCCESS)
>> + iommu_tce_xchg(tbl, entry, &hpa, &dir);
>> +
>> + return ret;
>> +}
>> +
>> +long kvmppc_tce_iommu_map(struct kvm *kvm, struct iommu_table *tbl,
>> + unsigned long entry, unsigned long gpa,
>> + enum dma_data_direction dir)
>> +{
>> + long ret;
>> + unsigned long hpa, ua, *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;
>> +
>> + if (kvmppc_gpa_to_ua(kvm, gpa, &ua, NULL))
>> + return H_PARAMETER;
>> +
>> + mem = mm_iommu_lookup(kvm->mm, ua, 1ULL << tbl->it_page_shift);
>> + if (!mem)
>> + return H_TOO_HARD;
>> +
>> + if (mm_iommu_ua_to_hpa(mem, ua, &hpa))
>> + return H_HARDWARE;
>
> IIUC this would happen if qemu had failed to preregister all of guest
> RAM, making this indeed an H_HARDWARE.

If QEMU failed to preregister, then mm_iommu_lookup() fails and it is
TOO_HARD. mm_iommu_ua_to_hpa() in this context cannot possibly fail (unless
broken memory) as it only returns error when out of bounds but
mm_iommu_lookup() ensures this.

>
>> + if (mm_iommu_mapped_inc(mem))
>> + return H_HARDWARE;
>
> I'm less clear on when this one would happen.

This may happen when there is a race with mm_iommu_put().

>
>> +
>> + ret = iommu_tce_xchg(tbl, entry, &hpa, &dir);
>> + if (ret) {
>> + mm_iommu_mapped_dec(mem);
>> + return H_TOO_HARD;
>> + }
>> +
>> + if (dir != DMA_NONE)
>> + kvmppc_tce_iommu_mapped_dec(kvm, tbl, entry);
>> +
>> + *pua = ua;
>> +
>> + return 0;
>> +}
>> +
>> long kvmppc_h_put_tce(struct kvm_vcpu *vcpu, unsigned long liobn,
>> unsigned long ioba, unsigned long tce)
>> {
>> struct kvmppc_spapr_tce_table *stt;
>> - long ret;
>> + long ret, idx;
>> + struct kvmppc_spapr_tce_iommu_table *stit;
>> + unsigned long entry, gpa;
>> + enum dma_data_direction dir;
>>
>> /* udbg_printf("H_PUT_TCE(): liobn=0x%lx ioba=0x%lx, tce=0x%lx\n", */
>> /* liobn, ioba, tce); */
>> @@ -230,6 +467,36 @@ long kvmppc_h_put_tce(struct kvm_vcpu *vcpu, unsigned long liobn,
>> if (ret != H_SUCCESS)
>> return ret;
>>
>> + stit = list_first_entry_or_null(&stt->iommu_tables,
>> + struct kvmppc_spapr_tce_iommu_table, next);
>> + if (stit) {
>> + entry = ioba >> stit->tbl->it_page_shift;
>> + gpa = tce & ~(TCE_PCI_READ | TCE_PCI_WRITE);
>> + dir = iommu_tce_direction(tce);
>> +
>> + if (dir == DMA_NONE) {
>> + if (iommu_tce_clear_param_check(stit->tbl, ioba, 0, 1))
>> + return H_PARAMETER;
>> + } else {
>> + if (iommu_tce_put_param_check(stit->tbl, ioba, gpa))
>
> Any way you could make these param check functions based on stt
> instead of stit->tbl? That would let you do them before checking if
> there are any hw tables to update, avaoiding the somewhat awkward
> if (at least one)
> for (each one)
> construct.

I could:
1. change iommu_tce_put_param_check() to take shift, offset, size and drop
use of IOMMU_PAGE_MASK(tbl) (and change all callers in vfio_iommu_spapr_tce.c);
2. make a copy of iommu_tce_put_param_check() which would take stt.

And yet this code does operate with tbl anyway, akward either way imho...

>
>> + return H_PARAMETER;
>> + }
>> +
>> + list_for_each_entry_lockless(stit, &stt->iommu_tables, next) {
>> + if (dir == DMA_NONE) {
>> + ret = kvmppc_tce_iommu_unmap(vcpu->kvm,
>> + stit->tbl, entry);
>> + } else {
>> + idx = srcu_read_lock(&vcpu->kvm->srcu);
>> + ret = kvmppc_tce_iommu_map(vcpu->kvm, stit->tbl,
>> + entry, gpa, dir);
>> + srcu_read_unlock(&vcpu->kvm->srcu, idx);
>> + }
>> + if (ret != H_SUCCESS)
>> + return ret;
>
> Doesn't this error path need to clean up for the case where you
> managed to update some backing TCE tables, but then failed later ones?

Probably.

This is what I asked in:
Re: [PATCH kernel v4 08/10] KVM: PPC: Separate TCE validation from update

Failure to update a hardware TCE table means we are in deep trouble, I
cannot think of any valid reason how we could get this far and not fail
before but fail now.

>
>> + }
>> + }
>> +
>> kvmppc_tce_put(stt, ioba >> stt->page_shift, tce);
>>
>> return H_SUCCESS;
>> @@ -242,9 +509,10 @@ long kvmppc_h_put_tce_indirect(struct kvm_vcpu *vcpu,
>> {
>> struct kvmppc_spapr_tce_table *stt;
>> long i, ret = H_SUCCESS, idx;
>> - unsigned long entry, ua = 0;
>> + unsigned long entry, gpa, ua = 0;
>> u64 __user *tces;
>> u64 tce;
>> + struct kvmppc_spapr_tce_iommu_table *stit;
>>
>> stt = kvmppc_find_table(vcpu->kvm, liobn);
>> if (!stt)
>> @@ -272,6 +540,9 @@ long kvmppc_h_put_tce_indirect(struct kvm_vcpu *vcpu,
>> }
>> tces = (u64 __user *) ua;
>>
>> + stit = list_first_entry_or_null(&stt->iommu_tables,
>> + struct kvmppc_spapr_tce_iommu_table, next);
>> +
>> for (i = 0; i < npages; ++i) {
>> if (get_user(tce, tces + i)) {
>> ret = H_TOO_HARD;
>> @@ -282,6 +553,15 @@ long kvmppc_h_put_tce_indirect(struct kvm_vcpu *vcpu,
>> ret = kvmppc_tce_validate(stt, tce);
>> if (ret != H_SUCCESS)
>> goto unlock_exit;
>> +
>> + if (stit) {
>> + gpa = tce & ~(TCE_PCI_READ | TCE_PCI_WRITE);
>> + ret = iommu_tce_put_param_check(stit->tbl,
>> + ioba + (i << stit->tbl->it_page_shift),
>> + gpa);
>> + if (ret != H_SUCCESS)
>> + goto unlock_exit;
>> + }
>> }
>>
>> for (i = 0; i < npages; ++i) {
>> @@ -291,6 +571,21 @@ long kvmppc_h_put_tce_indirect(struct kvm_vcpu *vcpu,
>> }
>> tce = be64_to_cpu(tce);
>>
>> + if (stit) {
>> + for (i = 0; i < npages; ++i) {
>> + gpa = tce & ~(TCE_PCI_READ | TCE_PCI_WRITE);
>> +
>> + list_for_each_entry_lockless(stit,
>> + &stt->iommu_tables, next) {
>> + ret = kvmppc_tce_iommu_map(vcpu->kvm,
>> + stit->tbl, entry + i, gpa,
>> + iommu_tce_direction(tce));
>> + if (ret != H_SUCCESS)
>> + goto unlock_exit;
>> + }
>
> Um.. what value will this for_each leave in stit after completion? I
> suspect it will be something bogus, which means re-using stit in the
> next 0..npages loop iteration won't be safe (you only initialize stit
> with the first entry outside that loop).

#define list_for_each_entry_lockless(pos, head, member) \
for (pos = list_entry_lockless((head)->next, typeof(*pos), member); \
&pos->member != (head); \
pos = list_entry_lockless(pos->member.next, typeof(*pos), member))

stit is "pos" which is reset every time the loop is called.

>
>> + }
>> + }
>> +
>> kvmppc_tce_put(stt, entry + i, tce);
>> }
>>
>> @@ -307,6 +602,7 @@ long kvmppc_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)
>> @@ -320,6 +616,25 @@ long kvmppc_h_stuff_tce(struct kvm_vcpu *vcpu,
>> if (tce_value & (TCE_PCI_WRITE | TCE_PCI_READ))
>> return H_PARAMETER;
>>
>> + stit = list_first_entry_or_null(&stt->iommu_tables,
>> + struct kvmppc_spapr_tce_iommu_table, next);
>> + if (stit) {
>> + if (iommu_tce_clear_param_check(stit->tbl, ioba,
>> + tce_value, npages))
>> + 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_tce_iommu_unmap(vcpu->kvm,
>> + stit->tbl, entry + i);
>> + if (ret)
>> + return ret;
>
> Again do you need some sort of cleanup for partial completion?

Again,
Re: [PATCH kernel v4 08/10] KVM: PPC: Separate TCE validation from update

This is an unexpected failure which should not happen, what kind of cleanup
it would make sense to do here? Re-map what was mapped before H_STUFF_TCE
was called?

>
>
>> + }
>> + }
>> + }
>> +
>> 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/book3s_64_vio_hv.c b/arch/powerpc/kvm/book3s_64_vio_hv.c
>> index dc1c66fda941..018c7d94a575 100644
>> --- a/arch/powerpc/kvm/book3s_64_vio_hv.c
>> +++ b/arch/powerpc/kvm/book3s_64_vio_hv.c
>> @@ -178,11 +178,104 @@ long kvmppc_gpa_to_ua(struct kvm *kvm, unsigned long gpa,
>> EXPORT_SYMBOL_GPL(kvmppc_gpa_to_ua);
>>
>> #ifdef CONFIG_KVM_BOOK3S_HV_POSSIBLE
>> +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 (!pua)
>> + return H_HARDWARE;
>> +
>> + pua = (void *) vmalloc_to_phys(pua);
>> + if (!pua)
>> + return H_TOO_HARD;
>> +
>> + 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;
>> +
>> + 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;
>> +}
>> +
>> +long kvmppc_rm_tce_iommu_map(struct kvm_vcpu *vcpu, struct iommu_table *tbl,
>> + unsigned long entry, unsigned long gpa,
>> + enum dma_data_direction dir)
>> +{
>> + long ret;
>> + unsigned long hpa = 0, ua;
>> + 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;
>> +
>> + if (kvmppc_gpa_to_ua(vcpu->kvm, gpa, &ua, NULL))
>> + return H_PARAMETER;
>> +
>> + mem = mm_iommu_lookup_rm(vcpu->kvm->mm, ua, 1ULL << tbl->it_page_shift);
>> + if (!mem)
>> + return H_TOO_HARD;
>> +
>> + if (mm_iommu_ua_to_hpa_rm(mem, ua, &hpa))
>> + return H_HARDWARE;
>> +
>> + pua = (void *) vmalloc_to_phys(pua);
>> + if (!pua)
>> + return H_HARDWARE;
>
> What circumstances can this fail under? Does it need to be H_TOO_HARD instead?

When kernel memory gets corrupted and vmalloc_to_page() won't be able to
find a page which was allocated with vmalloc.

>> +
>> + if (mm_iommu_mapped_inc(mem))
>> + return H_HARDWARE;
>> +
>> + ret = iommu_tce_xchg_rm(tbl, entry, &hpa, &dir);
>> + if (ret) {
>> + mm_iommu_mapped_dec(mem);
>> + return H_TOO_HARD;
>> + }
>> +
>> + if (dir != DMA_NONE)
>> + kvmppc_rm_tce_iommu_mapped_dec(vcpu->kvm, tbl, entry);
>> +
>> + *pua = ua;
>> +
>> + return 0;
>> +}
>> +EXPORT_SYMBOL_GPL(kvmppc_rm_tce_iommu_map);
>> +
>> 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, gpa;
>> + enum dma_data_direction dir;
>>
>> /* udbg_printf("H_PUT_TCE(): liobn=0x%lx ioba=0x%lx, tce=0x%lx\n", */
>> /* liobn, ioba, tce); */
>> @@ -199,6 +292,33 @@ long kvmppc_rm_h_put_tce(struct kvm_vcpu *vcpu, unsigned long liobn,
>> if (ret != H_SUCCESS)
>> return ret;
>>
>> + stit = list_first_entry_or_null(&stt->iommu_tables,
>> + struct kvmppc_spapr_tce_iommu_table, next);
>> + if (stit) {
>> + entry = ioba >> stit->tbl->it_page_shift;
>> + gpa = tce & ~(TCE_PCI_READ | TCE_PCI_WRITE);
>> + dir = iommu_tce_direction(tce);
>> +
>> + if (dir == DMA_NONE) {
>> + if (iommu_tce_clear_param_check(stit->tbl, ioba, 0, 1))
>> + return H_PARAMETER;
>> + } else {
>> + if (iommu_tce_put_param_check(stit->tbl, ioba, gpa))
>> + return H_PARAMETER;
>> + }
>> +
>> + 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, stit->tbl,
>> + entry, gpa, dir);
>> + if (ret != H_SUCCESS)
>> + return ret;
>> + }
>> + }
>> +
>> kvmppc_tce_put(stt, ioba >> stt->page_shift, tce);
>>
>> return H_SUCCESS;
>> @@ -237,9 +357,10 @@ long kvmppc_rm_h_put_tce_indirect(struct kvm_vcpu *vcpu,
>> {
>> struct kvmppc_spapr_tce_table *stt;
>> long i, ret = H_SUCCESS;
>> - unsigned long tces, entry, tce, ua = 0;
>> + unsigned long tces, entry, gpa, tce, 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)
>> @@ -303,17 +424,45 @@ long kvmppc_rm_h_put_tce_indirect(struct kvm_vcpu *vcpu,
>> }
>> }
>>
>> + stit = list_first_entry_or_null(&stt->iommu_tables,
>> + struct kvmppc_spapr_tce_iommu_table, next);
>> +
>> for (i = 0; i < npages; ++i) {
>> tce = be64_to_cpu(((u64 *)tces)[i]);
>>
>> ret = kvmppc_tce_validate(stt, tce);
>> if (ret != H_SUCCESS)
>> goto unlock_exit;
>> +
>> + if (stit) {
>> + gpa = tce & ~(TCE_PCI_READ | TCE_PCI_WRITE);
>> + ret = iommu_tce_put_param_check(stit->tbl,
>> + ioba + (i << stit->tbl->it_page_shift),
>> + gpa);
>> + if (ret != H_SUCCESS)
>> + goto unlock_exit;
>> +
>> + }
>> }
>>
>> for (i = 0; i < npages; ++i) {
>> tce = be64_to_cpu(((u64 *)tces)[i]);
>
> As noted in the earlier patch this is really dangerous - by reloading
> the tce from userspace you've thrown away the verification above.

Sure, I am adding a tces cache to kvm_vcpu.

>> + if (stit) {
>> + for (i = 0; i < npages; ++i) {
>> + gpa = tce & ~(TCE_PCI_READ | TCE_PCI_WRITE);
>> +
>> + list_for_each_entry_lockless(stit,
>> + &stt->iommu_tables, next) {
>> + ret = kvmppc_rm_tce_iommu_map(vcpu,
>> + stit->tbl, entry + i, gpa,
>> + iommu_tce_direction(tce));
>> + if (ret != H_SUCCESS)
>> + goto unlock_exit;
>> + }
>> + }
>> + }
>> +
>> kvmppc_tce_put(stt, entry + i, tce);
>> }
>>
>> @@ -330,6 +479,8 @@ 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)
>> @@ -343,6 +494,25 @@ long kvmppc_rm_h_stuff_tce(struct kvm_vcpu *vcpu,
>> if (tce_value & (TCE_PCI_WRITE | TCE_PCI_READ))
>> return H_PARAMETER;
>>
>> + stit = list_first_entry_or_null(&stt->iommu_tables,
>> + struct kvmppc_spapr_tce_iommu_table, next);
>> + if (stit) {
>> + if (iommu_tce_clear_param_check(stit->tbl, ioba,
>> + tce_value, npages))
>> + 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)
>> + return ret;
>> + }
>> + }
>> + }
>> +
>> 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 cd892dec7cb6..f3127dc87912 100644
>> --- a/arch/powerpc/kvm/powerpc.c
>> +++ b/arch/powerpc/kvm/powerpc.c
>> @@ -536,6 +536,8 @@ 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 */
>
> I'm not sure why this one should get a fallthrough comment, when none
> of the other cases do.

I believe it was either ignored then or checkpatch.pl did not warn about
this at the time.

>
>> + 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);
>> +
>
>
> Is there any particular reason you unwrap the group fd here, but the
> table fd inside kvm__spapr_tce_attach_iommu_group()?

No particular reason, just an intention not to spread too much spapr to KVM
VFIO device and vfio_group to POWER KVM.

I only unwrapp table_fd to see if it is in the kvm->arch.spapr_tce_tables
list, I am trying to keep spapr_tce_tables and kvmppc_spapr_tce_iommu_table
local to arch/powerpc/kvm/book3s_64_vio*.c

Unwrapping groupfd in arch/powerpc/kvm/book3s_64_vio*.c would mean
duplicating all kvm_vfio_group_get_external_user()/etc stubs in
arch/powerpc/kvm/book3s_64_vio.c, I did not want to duplicate these stubs.
I could but since I already have vfio_group unwrapped here, it seems
pointless to unwrap it over again in arch/powerpc/kvm/book3s_64_vio.c,
should I?

>
>> + 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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