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Message-ID: <51DC9CDA.3070906@ozlabs.ru>
Date: Wed, 10 Jul 2013 09:29:30 +1000
From: Alexey Kardashevskiy <aik@...abs.ru>
To: Alexander Graf <agraf@...e.de>
CC: linuxppc-dev@...ts.ozlabs.org,
David Gibson <david@...son.dropbear.id.au>,
Benjamin Herrenschmidt <benh@...nel.crashing.org>,
Paul Mackerras <paulus@...ba.org>,
Alex Williamson <alex.williamson@...hat.com>,
kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
kvm-ppc@...r.kernel.org
Subject: Re: [PATCH 8/8] KVM: PPC: Add hugepage support for IOMMU in-kernel
handling
On 07/10/2013 03:32 AM, Alexander Graf wrote:
> On 07/06/2013 05:07 PM, Alexey Kardashevskiy wrote:
>> This adds special support for huge pages (16MB). The reference
>> counting cannot be easily done for such pages in real mode (when
>> MMU is off) so we added a list of huge pages. It is populated in
>> virtual mode and get_page is called just once per a huge page.
>> Real mode handlers check if the requested page is huge and in the list,
>> then no reference counting is done, otherwise an exit to virtual mode
>> happens. The list is released at KVM exit. At the moment the fastest
>> card available for tests uses up to 9 huge pages so walking through this
>> list is not very expensive. However this can change and we may want
>> to optimize this.
>>
>> Signed-off-by: Paul Mackerras<paulus@...ba.org>
>> Signed-off-by: Alexey Kardashevskiy<aik@...abs.ru>
>>
>> ---
>>
>> Changes:
>> 2013/06/27:
>> * list of huge pages replaces with hashtable for better performance
>
> So the only thing your patch description really talks about is not true
> anymore?
>
>> * spinlock removed from real mode and only protects insertion of new
>> huge [ages descriptors into the hashtable
>>
>> 2013/06/05:
>> * fixed compile error when CONFIG_IOMMU_API=n
>>
>> 2013/05/20:
>> * the real mode handler now searches for a huge page by gpa (used to be pte)
>> * the virtual mode handler prints warning if it is called twice for the same
>> huge page as the real mode handler is expected to fail just once - when a
>> huge
>> page is not in the list yet.
>> * the huge page is refcounted twice - when added to the hugepage list and
>> when used in the virtual mode hcall handler (can be optimized but it will
>> make the patch less nice).
>>
>> Signed-off-by: Alexey Kardashevskiy<aik@...abs.ru>
>> ---
>> arch/powerpc/include/asm/kvm_host.h | 25 +++++++++
>> arch/powerpc/kernel/iommu.c | 6 ++-
>> arch/powerpc/kvm/book3s_64_vio.c | 104
>> +++++++++++++++++++++++++++++++++---
>> arch/powerpc/kvm/book3s_64_vio_hv.c | 21 ++++++--
>> 4 files changed, 146 insertions(+), 10 deletions(-)
>>
>> diff --git a/arch/powerpc/include/asm/kvm_host.h
>> b/arch/powerpc/include/asm/kvm_host.h
>> index 53e61b2..a7508cf 100644
>> --- a/arch/powerpc/include/asm/kvm_host.h
>> +++ b/arch/powerpc/include/asm/kvm_host.h
>> @@ -30,6 +30,7 @@
>> #include<linux/kvm_para.h>
>> #include<linux/list.h>
>> #include<linux/atomic.h>
>> +#include<linux/hashtable.h>
>> #include<asm/kvm_asm.h>
>> #include<asm/processor.h>
>> #include<asm/page.h>
>> @@ -182,10 +183,34 @@ struct kvmppc_spapr_tce_table {
>> u32 window_size;
>> struct iommu_group *grp; /* used for IOMMU groups */
>> struct vfio_group *vfio_grp; /* used for IOMMU groups */
>> + DECLARE_HASHTABLE(hash_tab, ilog2(64)); /* used for IOMMU groups */
>> + spinlock_t hugepages_write_lock; /* used for IOMMU groups */
>> struct { struct { unsigned long put, indir, stuff; } rm, vm; } stat;
>> struct page *pages[0];
>> };
>>
>> +/*
>> + * The KVM guest can be backed with 16MB pages.
>> + * In this case, we cannot do page counting from the real mode
>> + * as the compound pages are used - they are linked in a list
>> + * with pointers as virtual addresses which are inaccessible
>> + * in real mode.
>> + *
>> + * The code below keeps a 16MB pages list and uses page struct
>> + * in real mode if it is already locked in RAM and inserted into
>> + * the list or switches to the virtual mode where it can be
>> + * handled in a usual manner.
>> + */
>> +#define KVMPPC_SPAPR_HUGEPAGE_HASH(gpa) hash_32(gpa>> 24, 32)
>> +
>> +struct kvmppc_spapr_iommu_hugepage {
>> + struct hlist_node hash_node;
>> + unsigned long gpa; /* Guest physical address */
>> + unsigned long hpa; /* Host physical address */
>> + struct page *page; /* page struct of the very first subpage */
>> + unsigned long size; /* Huge page size (always 16MB at the moment) */
>> +};
>> +
>> struct kvmppc_linear_info {
>> void *base_virt;
>> unsigned long base_pfn;
>> diff --git a/arch/powerpc/kernel/iommu.c b/arch/powerpc/kernel/iommu.c
>> index 51678ec..e0b6eca 100644
>> --- a/arch/powerpc/kernel/iommu.c
>> +++ b/arch/powerpc/kernel/iommu.c
>> @@ -999,7 +999,8 @@ int iommu_free_tces(struct iommu_table *tbl, unsigned
>> long entry,
>> if (!pg) {
>> ret = -EAGAIN;
>> } else if (PageCompound(pg)) {
>> - ret = -EAGAIN;
>> + /* Hugepages will be released at KVM exit */
>> + ret = 0;
>> } else {
>> if (oldtce& TCE_PCI_WRITE)
>> SetPageDirty(pg);
>> @@ -1009,6 +1010,9 @@ int iommu_free_tces(struct iommu_table *tbl,
>> unsigned long entry,
>> struct page *pg = pfn_to_page(oldtce>> PAGE_SHIFT);
>> if (!pg) {
>> ret = -EAGAIN;
>> + } else if (PageCompound(pg)) {
>> + /* Hugepages will be released at KVM exit */
>> + ret = 0;
>> } else {
>> if (oldtce& TCE_PCI_WRITE)
>> SetPageDirty(pg);
>> diff --git a/arch/powerpc/kvm/book3s_64_vio.c
>> b/arch/powerpc/kvm/book3s_64_vio.c
>> index 2b51f4a..c037219 100644
>> --- a/arch/powerpc/kvm/book3s_64_vio.c
>> +++ b/arch/powerpc/kvm/book3s_64_vio.c
>> @@ -46,6 +46,40 @@
>>
>> #define ERROR_ADDR ((void *)~(unsigned long)0x0)
>>
>> +#ifdef CONFIG_IOMMU_API
>
> Can't you just make CONFIG_IOMMU_API mandatory in Kconfig?
Sure I can. I can do anything. Why should I? Do I have to do that to get
this accepted? I do not understand this comment. It has already been
discussed how to enable this option.
>> +static void kvmppc_iommu_hugepages_init(struct kvmppc_spapr_tce_table *tt)
>> +{
>> + spin_lock_init(&tt->hugepages_write_lock);
>> + hash_init(tt->hash_tab);
>> +}
>> +
>> +static void kvmppc_iommu_hugepages_cleanup(struct kvmppc_spapr_tce_table
>> *tt)
>> +{
>> + int bkt;
>> + struct kvmppc_spapr_iommu_hugepage *hp;
>> + struct hlist_node *tmp;
>> +
>> + spin_lock(&tt->hugepages_write_lock);
>> + hash_for_each_safe(tt->hash_tab, bkt, tmp, hp, hash_node) {
>> + pr_debug("Release HP liobn=%llx #%u gpa=%lx hpa=%lx size=%ld\n",
>> + tt->liobn, bkt, hp->gpa, hp->hpa, hp->size);
>
> trace point
>
>> + hlist_del_rcu(&hp->hash_node);
>> +
>> + put_page(hp->page);
>
> Don't you have to mark them dirty?
get_user_pages_fast is called with writing==1. Does not it do the same?
>
>> + kfree(hp);
>> + }
>> + spin_unlock(&tt->hugepages_write_lock);
>> +}
>> +#else
>> +static void kvmppc_iommu_hugepages_init(struct kvmppc_spapr_tce_table *tt)
>> +{
>> +}
>> +
>> +static void kvmppc_iommu_hugepages_cleanup(struct kvmppc_spapr_tce_table
>> *tt)
>> +{
>> +}
>> +#endif /* CONFIG_IOMMU_API */
>> +
>> static long kvmppc_stt_npages(unsigned long window_size)
>> {
>> return ALIGN((window_size>> SPAPR_TCE_SHIFT)
>> @@ -112,6 +146,7 @@ static void release_spapr_tce_table(struct
>> kvmppc_spapr_tce_table *stt)
>>
>> mutex_lock(&kvm->lock);
>> list_del(&stt->list);
>> + kvmppc_iommu_hugepages_cleanup(stt);
>>
>> #ifdef CONFIG_IOMMU_API
>> if (stt->grp) {
>> @@ -200,6 +235,7 @@ long kvm_vm_ioctl_create_spapr_tce(struct kvm *kvm,
>> kvm_get_kvm(kvm);
>>
>> mutex_lock(&kvm->lock);
>> + kvmppc_iommu_hugepages_init(stt);
>> list_add(&stt->list,&kvm->arch.spapr_tce_tables);
>>
>> mutex_unlock(&kvm->lock);
>> @@ -283,6 +319,7 @@ long kvm_vm_ioctl_create_spapr_tce_iommu(struct kvm
>> *kvm,
>>
>> kvm_get_kvm(kvm);
>> mutex_lock(&kvm->lock);
>> + kvmppc_iommu_hugepages_init(tt);
>> list_add(&tt->list,&kvm->arch.spapr_tce_tables);
>> mutex_unlock(&kvm->lock);
>>
>> @@ -307,10 +344,17 @@ long kvm_vm_ioctl_create_spapr_tce_iommu(struct kvm
>> *kvm,
>>
>> /* Converts guest physical address to host virtual address */
>> static void __user *kvmppc_vm_gpa_to_hva_and_get(struct kvm_vcpu *vcpu,
>> + struct kvmppc_spapr_tce_table *tt,
>> unsigned long gpa, struct page **pg, unsigned long *hpa)
>> {
>> unsigned long hva, gfn = gpa>> PAGE_SHIFT;
>> struct kvm_memory_slot *memslot;
>> +#ifdef CONFIG_IOMMU_API
>> + struct kvmppc_spapr_iommu_hugepage *hp;
>> + unsigned key = KVMPPC_SPAPR_HUGEPAGE_HASH(gpa);
>> + pte_t *ptep;
>> + unsigned int shift = 0;
>> +#endif
>>
>> memslot = search_memslots(kvm_memslots(vcpu->kvm), gfn);
>> if (!memslot)
>> @@ -325,6 +369,54 @@ static void __user
>> *kvmppc_vm_gpa_to_hva_and_get(struct kvm_vcpu *vcpu,
>> *hpa = __pa((unsigned long) page_address(*pg)) +
>> (hva& ~PAGE_MASK);
>>
>> +#ifdef CONFIG_IOMMU_API
>
> This function is becoming incredibly large. Please split it up. Also please
> document the code.
Less than 100 lines is incredibly large? There are _many_ functions bigger
than that. I do not really see the point in making a separate function
which is going to be called only once.
--
Alexey
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