[PATCH kernel] KVM: PPC: Align the table size to system page size

[PATCH kernel] KVM: PPC: Align the table size to system page size

[Alexey Kardashevskiy]

At the moment the userspace can request a table smaller than a page size
and this value will be stored as kvmppc_spapr_tce_table::size.
However the actual allocated size will still be aligned to the system
page size as alloc_page() is used there.

This aligns the table size up to the system page size. It should not
change the existing behaviour but when in-kernel TCE acceleration patchset
reaches the upstream kernel, this will allow small TCE tables be
accelerated as well: PCI IODA iommu_table allocator already aligns
the size and, without this patch, an IOMMU group won't attach to LIOBN
due to the mismatching table size.

Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
---

For sake of bisectability (otherwise in-kernel acceleration won't work
hugepages braking DMA completely), this is better be put before
[PATCH kernel v11 00/10] powerpc/kvm/vfio: Enable in-kernel acceleration

---
 arch/powerpc/kvm/book3s_64_vio.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/powerpc/kvm/book3s_64_vio.c b/arch/powerpc/kvm/book3s_64_vio.c
index aea3a5b74fb6..45941af9c6d7 100644
--- a/arch/powerpc/kvm/book3s_64_vio.c
+++ b/arch/powerpc/kvm/book3s_64_vio.c
@@ -333,7 +333,7 @@ long kvm_vm_ioctl_create_spapr_tce(struct kvm *kvm,
 			return -EBUSY;
 	}
 
-	size = args->size;
+	size = _ALIGN_UP(args->size, PAGE_SIZE >> 3);
 	npages = kvmppc_tce_pages(size);
 	ret = kvmppc_account_memlimit(kvmppc_stt_pages(npages), true);
 	if (ret) {
-- 
2.11.0

Re: [PATCH kernel] KVM: PPC: Align the table size to system page size

[David Gibson]

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On Thu, Apr 13, 2017 at 05:04:20PM +1000, Alexey Kardashevskiy wrote:
> At the moment the userspace can request a table smaller than a page size
> and this value will be stored as kvmppc_spapr_tce_table::size.
> However the actual allocated size will still be aligned to the system
> page size as alloc_page() is used there.
> 
> This aligns the table size up to the system page size. It should not
> change the existing behaviour but when in-kernel TCE acceleration patchset
> reaches the upstream kernel, this will allow small TCE tables be
> accelerated as well: PCI IODA iommu_table allocator already aligns
> the size and, without this patch, an IOMMU group won't attach to LIOBN
> due to the mismatching table size.
> 
> Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>

Reviewed-by: David Gibson <david@gibson.dropbear.id.au>

> ---
> 
> For sake of bisectability (otherwise in-kernel acceleration won't work
> hugepages braking DMA completely), this is better be put before
> [PATCH kernel v11 00/10] powerpc/kvm/vfio: Enable in-kernel acceleration
> 
> ---
>  arch/powerpc/kvm/book3s_64_vio.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/powerpc/kvm/book3s_64_vio.c b/arch/powerpc/kvm/book3s_64_vio.c
> index aea3a5b74fb6..45941af9c6d7 100644
> --- a/arch/powerpc/kvm/book3s_64_vio.c
> +++ b/arch/powerpc/kvm/book3s_64_vio.c
> @@ -333,7 +333,7 @@ long kvm_vm_ioctl_create_spapr_tce(struct kvm *kvm,
>  			return -EBUSY;
>  	}
>  
> -	size = args->size;
> +	size = _ALIGN_UP(args->size, PAGE_SIZE >> 3);
>  	npages = kvmppc_tce_pages(size);
>  	ret = kvmppc_account_memlimit(kvmppc_stt_pages(npages), true);
>  	if (ret) {

-- 
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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