[PATCH kernel] KVM: PPC: Allocate guest TCEs on demand too
David Gibson
david at gibson.dropbear.id.au
Thu Feb 28 11:15:46 AEDT 2019
On Wed, Feb 27, 2019 at 07:42:35PM +1100, Alexey Kardashevskiy wrote:
> We already allocate hardware TCE tables in multiple levels and skip
> intermediate levels when we can, now it is a turn of the KVM TCE tables.
> Thankfully these are allocated already in 2 levels.
>
> This moves the table's last level allocation from the creating helper to
> kvmppc_tce_put() and kvm_spapr_tce_fault().
>
> This adds kvmppc_rm_ioba_validate() to do an additional test if
> the consequent kvmppc_tce_put() needs a page which has not been allocated;
> if this is the case, we bail out to virtual mode handlers.
>
> Signed-off-by: Alexey Kardashevskiy <aik at ozlabs.ru>
Reviewed-by: David Gibson <david at gibson.dropbear.id.au>
> ---
>
> For NVLink2 passthrough guests with 128TiB DMA windows (when we push GPU RAM
> above the PCI MMIO window in the guest) and very fragmented system RAM
> the difference is about 16GiB of RAM before and after this patch.
>
> ---
> arch/powerpc/kvm/book3s_64_vio.c | 21 ++++------
> arch/powerpc/kvm/book3s_64_vio_hv.c | 62 ++++++++++++++++++++++++++---
> 2 files changed, 64 insertions(+), 19 deletions(-)
>
> diff --git a/arch/powerpc/kvm/book3s_64_vio.c b/arch/powerpc/kvm/book3s_64_vio.c
> index f02b049..281b56b 100644
> --- a/arch/powerpc/kvm/book3s_64_vio.c
> +++ b/arch/powerpc/kvm/book3s_64_vio.c
> @@ -228,7 +228,8 @@ static void release_spapr_tce_table(struct rcu_head *head)
> unsigned long i, npages = kvmppc_tce_pages(stt->size);
>
> for (i = 0; i < npages; i++)
> - __free_page(stt->pages[i]);
> + if (stt->pages[i])
> + __free_page(stt->pages[i]);
>
> kfree(stt);
> }
> @@ -241,6 +242,12 @@ static vm_fault_t kvm_spapr_tce_fault(struct vm_fault *vmf)
> if (vmf->pgoff >= kvmppc_tce_pages(stt->size))
> return VM_FAULT_SIGBUS;
>
> + if (!stt->pages[vmf->pgoff]) {
> + stt->pages[vmf->pgoff] = alloc_page(GFP_KERNEL | __GFP_ZERO);
> + if (!stt->pages[vmf->pgoff])
> + return VM_FAULT_OOM;
> + }
> +
> page = stt->pages[vmf->pgoff];
> get_page(page);
> vmf->page = page;
> @@ -296,7 +303,6 @@ long kvm_vm_ioctl_create_spapr_tce(struct kvm *kvm,
> struct kvmppc_spapr_tce_table *siter;
> unsigned long npages, size = args->size;
> int ret = -ENOMEM;
> - int i;
>
> if (!args->size || args->page_shift < 12 || args->page_shift > 34 ||
> (args->offset + args->size > (ULLONG_MAX >> args->page_shift)))
> @@ -320,12 +326,6 @@ long kvm_vm_ioctl_create_spapr_tce(struct kvm *kvm,
> 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);
> - if (!stt->pages[i])
> - goto fail;
> - }
> -
> mutex_lock(&kvm->lock);
>
> /* Check this LIOBN hasn't been previously allocated */
> @@ -352,11 +352,6 @@ long kvm_vm_ioctl_create_spapr_tce(struct kvm *kvm,
> if (ret >= 0)
> return ret;
>
> - fail:
> - for (i = 0; i < npages; i++)
> - if (stt->pages[i])
> - __free_page(stt->pages[i]);
> -
> kfree(stt);
> fail_acct:
> kvmppc_account_memlimit(kvmppc_stt_pages(npages), false);
> diff --git a/arch/powerpc/kvm/book3s_64_vio_hv.c b/arch/powerpc/kvm/book3s_64_vio_hv.c
> index 2206bc7..fbb920d 100644
> --- a/arch/powerpc/kvm/book3s_64_vio_hv.c
> +++ b/arch/powerpc/kvm/book3s_64_vio_hv.c
> @@ -158,23 +158,69 @@ static u64 *kvmppc_page_address(struct page *page)
> return (u64 *) page_address(page);
> }
>
> +/*
> + * TCEs pages are allocated in kvmppc_tce_put() which won't be able to do so
> + * in real mode.
> + * Check if kvmppc_tce_put() can succeed in real mode, i.e. a TCEs page is
> + * allocated or not required (when clearing a tce entry).
> + */
> +static long kvmppc_rm_ioba_validate(struct kvmppc_spapr_tce_table *stt,
> + unsigned long ioba, unsigned long npages, bool clearing)
> +{
> + unsigned long i, sttpage, sttpages;
> + unsigned long ret = kvmppc_ioba_validate(stt, ioba, npages);
> +
> + if (ret)
> + return ret;
> + /*
> + * clearing==true says kvmppc_tce_put won't be allocating pages
> + * for empty tces.
> + */
> + if (clearing)
> + return H_SUCCESS;
> +
> + sttpage = ((ioba >> stt->page_shift) - stt->offset) / TCES_PER_PAGE;
> + sttpages = (npages + TCES_PER_PAGE - 1) / TCES_PER_PAGE;
> + for (i = sttpage; i < sttpage + sttpages; ++i)
> + if (!stt->pages[i])
> + return H_TOO_HARD;
> +
> + return H_SUCCESS;
> +}
> +
> /*
> * Handles TCE requests for emulated devices.
> * Puts guest TCE values to the table and expects user space to convert them.
> * Called in both real and virtual modes.
> * Cannot fail so kvmppc_tce_validate must be called before it.
> *
> - * WARNING: This will be called in real-mode on HV KVM and virtual
> - * mode on PR KVM
> + * WARNING: This will be called in real-mode on HV HPT KVM and virtual
> + * mode on PR KVM or HV radix KVM
> */
> void kvmppc_tce_put(struct kvmppc_spapr_tce_table *stt,
> unsigned long idx, unsigned long tce)
> {
> struct page *page;
> u64 *tbl;
> + unsigned long sttpage;
>
> idx -= stt->offset;
> - page = stt->pages[idx / TCES_PER_PAGE];
> + sttpage = idx / TCES_PER_PAGE;
> + page = stt->pages[sttpage];
> +
> + if (!page) {
> + /* We allow any TCE, not just with read|write permissions */
> + if (!tce)
> + return;
> + /*
> + * We must not end up here in real mode,
> + * kvmppc_rm_ioba_validate() takes care of this.
> + */
> + page = alloc_page(GFP_KERNEL | __GFP_ZERO);
> + if (WARN_ON_ONCE(!page))
> + return;
> + stt->pages[sttpage] = page;
> + }
> tbl = kvmppc_page_address(page);
>
> tbl[idx % TCES_PER_PAGE] = tce;
> @@ -381,7 +427,7 @@ long kvmppc_rm_h_put_tce(struct kvm_vcpu *vcpu, unsigned long liobn,
> if (!stt)
> return H_TOO_HARD;
>
> - ret = kvmppc_ioba_validate(stt, ioba, 1);
> + ret = kvmppc_rm_ioba_validate(stt, ioba, 1, tce == 0);
> if (ret != H_SUCCESS)
> return ret;
>
> @@ -480,7 +526,7 @@ long kvmppc_rm_h_put_tce_indirect(struct kvm_vcpu *vcpu,
> if (tce_list & (SZ_4K - 1))
> return H_PARAMETER;
>
> - ret = kvmppc_ioba_validate(stt, ioba, npages);
> + ret = kvmppc_rm_ioba_validate(stt, ioba, npages, false);
> if (ret != H_SUCCESS)
> return ret;
>
> @@ -583,7 +629,7 @@ long kvmppc_rm_h_stuff_tce(struct kvm_vcpu *vcpu,
> if (!stt)
> return H_TOO_HARD;
>
> - ret = kvmppc_ioba_validate(stt, ioba, npages);
> + ret = kvmppc_rm_ioba_validate(stt, ioba, npages, tce_value == 0);
> if (ret != H_SUCCESS)
> return ret;
>
> @@ -635,6 +681,10 @@ long kvmppc_h_get_tce(struct kvm_vcpu *vcpu, unsigned long liobn,
>
> idx = (ioba >> stt->page_shift) - stt->offset;
> page = stt->pages[idx / TCES_PER_PAGE];
> + if (!page) {
> + vcpu->arch.regs.gpr[4] = 0;
> + return H_SUCCESS;
> + }
> tbl = (u64 *)page_address(page);
>
> vcpu->arch.regs.gpr[4] = tbl[idx % TCES_PER_PAGE];
--
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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