Re: [PATCH kernel 1/2] powerpc/powernv: Reuse existing TCE code for sketchy bypass

[Benjamin Herrenschmidt <benh@kernel.crashing.org>]

On Fri, 2018-06-01 at 18:10 +1000, Alexey Kardashevskiy wrote:
> The existing sketchy bypass ignores the existing default 32bit TCE table
> (created by default for every PE at boot time or after being used by
> VFIO) and it allocates another table instead without updating PE DMA
> config (pe->table_group). So if we decide to use such device for VFIO
> later, this new table will also leak memory.
> 
> This replaces adhoc table allocation and programming with the existing
> API which handles memory leaks.
> 
> This programs the default 32bit table back to TVE#0 if configuring
> the new table failed for some reason.
> 
> While we are at it, switch from the hardcoded 256MB TCEs to the biggest
> size supported by the hardware and reported by the firmware. This allows
> the sketchy bypass (originally made for POWER8 only) to work on POWER9
> too assuming that PHB4 type is defined and pnv_pci_ioda_dma_64bit_bypass()
> is called (coming next).

It won't work on POWER9 for other reasons. Mostly memory isn't
contiguous there.

What we shuld look into rather than removing the 32-bit table is
exploit DD2 P9 feature allowing to overlay TVE0 and TVE1 so that 0..4G
is in control of TVE0 and the rest goes to TVE1.
 
> This does not call iommu_init_table() for the new table as the caller
> will use &dma_nommu_ops and therefore ::it_map is not needed.
> 
> Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
> ---
> 
> Tested with:
>  	if (pe->tce_bypass_enabled) {
>  		top = pe->tce_bypass_base + memblock_end_of_DRAM() - 1;
> -		bypass = (dma_mask >= top);
> +		bypass = false;//(dma_mask >= top);
>  	}
> ---
>  arch/powerpc/platforms/powernv/pci-ioda.c | 71 +++++++++++++++++--------------
>  1 file changed, 39 insertions(+), 32 deletions(-)
> 
> diff --git a/arch/powerpc/platforms/powernv/pci-ioda.c b/arch/powerpc/platforms/powernv/pci-ioda.c
> index ceb7e64..9239142 100644
> --- a/arch/powerpc/platforms/powernv/pci-ioda.c
> +++ b/arch/powerpc/platforms/powernv/pci-ioda.c
> @@ -1791,54 +1791,61 @@ static bool pnv_pci_ioda_pe_single_vendor(struct pnv_ioda_pe *pe)
>   *
>   * Currently this will only work on PHB3 (POWER8).
>   */
> +static long pnv_pci_ioda2_create_table(struct iommu_table_group *table_group,
> +		int num, __u32 page_shift, __u64 window_size, __u32 levels,
> +		struct iommu_table **ptbl);
> +
> +static long pnv_pci_ioda2_set_window(struct iommu_table_group *table_group,
> +		int num, struct iommu_table *tbl);
> +
> +static unsigned long pnv_ioda_parse_tce_sizes(struct pnv_phb *phb);
> +
>  static int pnv_pci_ioda_dma_64bit_bypass(struct pnv_ioda_pe *pe)
>  {
> -	u64 window_size, table_size, tce_count, addr;
> -	struct page *table_pages;
> -	u64 tce_order = 28; /* 256MB TCEs */
> -	__be64 *tces;
> +	u64 window_size;
>  	s64 rc;
> +	struct iommu_table *tbl, *oldtbl = NULL;
> +	unsigned long shift, offset;
>  
>  	/*
>  	 * Window size needs to be a power of two, but needs to account for
>  	 * shifting memory by the 4GB offset required to skip 32bit space.
>  	 */
> -	window_size = roundup_pow_of_two(memory_hotplug_max() + (1ULL << 32));
> -	tce_count = window_size >> tce_order;
> -	table_size = tce_count << 3;
> -
> -	if (table_size < PAGE_SIZE)
> -		table_size = PAGE_SIZE;
> +	window_size = roundup_pow_of_two(memory_hotplug_max() + SZ_4G);
> +	shift = ilog2(pnv_ioda_parse_tce_sizes(pe->phb));
> +	rc = pnv_pci_ioda2_create_table(&pe->table_group, 0, shift, window_size,
> +			POWERNV_IOMMU_DEFAULT_LEVELS, &tbl);
> +	if (rc) {
> +		pe_err(pe, "Failed to create 64-bypass TCE table, err %ld", rc);
> +		return rc;
> +	}
>  
> -	table_pages = alloc_pages_node(pe->phb->hose->node, GFP_KERNEL,
> -				       get_order(table_size));
> -	if (!table_pages)
> +	offset = SZ_4G >> shift;
> +	rc = tbl->it_ops->set(tbl, offset, tbl->it_size - offset,
> +			0 /* uaddr */, DMA_BIDIRECTIONAL, 0 /* attrs */);
> +	if (rc)
>  		goto err;
>  
> -	tces = page_address(table_pages);
> -	if (!tces)
> +	if (pe->table_group.tables[0]) {
> +		oldtbl = pe->table_group.tables[0];
> +		pnv_pci_ioda2_unset_window(&pe->table_group, 0);
> +	}
> +
> +	rc = pnv_pci_ioda2_set_window(&pe->table_group, 0, tbl);
> +	if (rc != OPAL_SUCCESS) {
> +		rc = pnv_pci_ioda2_set_window(&pe->table_group, 0, oldtbl);
>  		goto err;
> +	}
>  
> -	memset(tces, 0, table_size);
> +	if (oldtbl)
> +		iommu_tce_table_put(oldtbl);
>  
> -	for (addr = 0; addr < memory_hotplug_max(); addr += (1 << tce_order)) {
> -		tces[(addr + (1ULL << 32)) >> tce_order] =
> -			cpu_to_be64(addr | TCE_PCI_READ | TCE_PCI_WRITE);
> -	}
> +	pe_info(pe, "Using 64-bit DMA iommu bypass (through TVE#0)\n");
> +	return 0;
>  
> -	rc = opal_pci_map_pe_dma_window(pe->phb->opal_id,
> -					pe->pe_number,
> -					/* reconfigure window 0 */
> -					(pe->pe_number << 1) + 0,
> -					1,
> -					__pa(tces),
> -					table_size,
> -					1 << tce_order);
> -	if (rc == OPAL_SUCCESS) {
> -		pe_info(pe, "Using 64-bit DMA iommu bypass (through TVE#0)\n");
> -		return 0;
> -	}
>  err:
> +	iommu_tce_table_put(tbl);
> +
>  	pe_err(pe, "Error configuring 64-bit DMA bypass\n");
>  	return -EIO;
>  }