Re: [PATCH kernel v2 2/2] KVM: PPC: Check if IOMMU page is contained in the pinned physical page

[David Gibson <david@gibson.dropbear.id.au>]

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On Tue, Jun 26, 2018 at 03:59:26PM +1000, Alexey Kardashevskiy wrote:
> We already have a check in drivers/vfio/vfio_iommu_spapr_tce.c that
> an IOMMU page is contained in the physical page so the PCI hardware won't
> get access to unassigned host memory.
> 
> However we do not have this check in KVM fastpath (H_PUT_TCE accelerated
> code) so the user space can pin memory backed with 64k pages and create
> a hardware TCE table with a bigger page size. We were lucky so far and
> did not hit this yet as the very first time the mapping happens
> we do not have tbl::it_userspace allocated yet and fall back to
> the userspace which in turn calls VFIO IOMMU driver and that fails
> because of the check in vfio_iommu_spapr_tce.c which is really
> sustainable solution.
> 
> This stores the smallest preregistered page size in the preregistered
> region descriptor and changes the mm_iommu_xxx API to check this against
> the IOMMU page size.
> 
> Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
> ---
> Changes:
> v2:
> * explicitly check for compound pages before calling compound_order()
> 
> ---
> The bug is: run QEMU _without_ hugepages (no -mempath) and tell it to
> advertise 16MB pages to the guest; a typical pseries guest will use 16MB
> for IOMMU pages without checking the mmu pagesize and this will fail
> at https://git.qemu.org/?p=qemu.git;a=blob;f=hw/vfio/common.c;h=fb396cf00ac40eb35967a04c9cc798ca896eed57;hb=refs/heads/master#l256
> 
> With the change, mapping will fail in KVM and the guest will print:
> 
> mlx5_core 0000:00:00.0: ibm,create-pe-dma-window(2027) 0 8000000 20000000 18 1f returned 0 (liobn = 0x80000001 starting addr = 8000000 0)
> mlx5_core 0000:00:00.0: created tce table LIOBN 0x80000001 for /pci@800000020000000/ethernet@0
> mlx5_core 0000:00:00.0: failed to map direct window for
> /pci@800000020000000/ethernet@0: -1

[snip]
> @@ -124,7 +125,7 @@ long mm_iommu_get(struct mm_struct *mm, unsigned long ua, unsigned long entries,
>  		struct mm_iommu_table_group_mem_t **pmem)
>  {
>  	struct mm_iommu_table_group_mem_t *mem;
> -	long i, j, ret = 0, locked_entries = 0;
> +	long i, j, ret = 0, locked_entries = 0, pageshift;
>  	struct page *page = NULL;
>  
>  	mutex_lock(&mem_list_mutex);
> @@ -166,6 +167,8 @@ long mm_iommu_get(struct mm_struct *mm, unsigned long ua, unsigned long entries,
>  		goto unlock_exit;
>  	}
>  
> +	mem->pageshift = 30; /* start from 1G pages - the biggest we have */

What about 16G pages on an HPT system?

>  	for (i = 0; i < entries; ++i) {
>  		if (1 != get_user_pages_fast(ua + (i << PAGE_SHIFT),
>  					1/* pages */, 1/* iswrite */, &page)) {
> @@ -199,6 +202,11 @@ long mm_iommu_get(struct mm_struct *mm, unsigned long ua, unsigned long entries,
>  			}
>  		}
>  populate:
> +		pageshift = PAGE_SHIFT;
> +		if (PageCompound(page))
> +			pageshift += compound_order(compound_head(page));
> +		mem->pageshift = min_t(unsigned int, mem->pageshift, pageshift);

Why not make mem->pageshift and pageshift local the same type to avoid
the min_t() ?

> +
>  		mem->hpas[i] = page_to_pfn(page) << PAGE_SHIFT;
>  	}
>  
> @@ -349,7 +357,7 @@ struct mm_iommu_table_group_mem_t *mm_iommu_find(struct mm_struct *mm,
>  EXPORT_SYMBOL_GPL(mm_iommu_find);
>  
>  long mm_iommu_ua_to_hpa(struct mm_iommu_table_group_mem_t *mem,
> -		unsigned long ua, unsigned long *hpa)
> +		unsigned long ua, unsigned int pageshift, unsigned long *hpa)
>  {
>  	const long entry = (ua - mem->ua) >> PAGE_SHIFT;
>  	u64 *va = &mem->hpas[entry];
> @@ -357,6 +365,9 @@ long mm_iommu_ua_to_hpa(struct mm_iommu_table_group_mem_t *mem,
>  	if (entry >= mem->entries)
>  		return -EFAULT;
>  
> +	if (pageshift > mem->pageshift)
> +		return -EFAULT;
> +
>  	*hpa = *va | (ua & ~PAGE_MASK);
>  
>  	return 0;
> @@ -364,7 +375,7 @@ long mm_iommu_ua_to_hpa(struct mm_iommu_table_group_mem_t *mem,
>  EXPORT_SYMBOL_GPL(mm_iommu_ua_to_hpa);
>  
>  long mm_iommu_ua_to_hpa_rm(struct mm_iommu_table_group_mem_t *mem,
> -		unsigned long ua, unsigned long *hpa)
> +		unsigned long ua, unsigned int pageshift, unsigned long *hpa)
>  {
>  	const long entry = (ua - mem->ua) >> PAGE_SHIFT;
>  	void *va = &mem->hpas[entry];
> @@ -373,6 +384,9 @@ long mm_iommu_ua_to_hpa_rm(struct mm_iommu_table_group_mem_t *mem,
>  	if (entry >= mem->entries)
>  		return -EFAULT;
>  
> +	if (pageshift > mem->pageshift)
> +		return -EFAULT;
> +
>  	pa = (void *) vmalloc_to_phys(va);
>  	if (!pa)
>  		return -EFAULT;
> diff --git a/drivers/vfio/vfio_iommu_spapr_tce.c b/drivers/vfio/vfio_iommu_spapr_tce.c
> index 2da5f05..7cd63b0 100644
> --- a/drivers/vfio/vfio_iommu_spapr_tce.c
> +++ b/drivers/vfio/vfio_iommu_spapr_tce.c
> @@ -467,7 +467,7 @@ static int tce_iommu_prereg_ua_to_hpa(struct tce_container *container,
>  	if (!mem)
>  		return -EINVAL;
>  
> -	ret = mm_iommu_ua_to_hpa(mem, tce, phpa);
> +	ret = mm_iommu_ua_to_hpa(mem, tce, shift, phpa);
>  	if (ret)
>  		return -EINVAL;
>  

-- 
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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