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Subject: Re: [PATCH v5 02/11] powerpc/kernel/iommu: Add new
 iommu_table_in_use() helper
To:     Leonardo Bras <leobras.c@gmail.com>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>,
        Alexey Kardashevskiy <aik@ozlabs.ru>,
        David Gibson <david@gibson.dropbear.id.au>,
        kernel test robot <lkp@intel.com>,
        Nicolin Chen <nicoleotsuka@gmail.com>
Cc:     linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org
References: <20210716082755.428187-1-leobras.c@gmail.com>
 <20210716082755.428187-3-leobras.c@gmail.com>
From:   Frederic Barrat <fbarrat@linux.ibm.com>
Message-ID: <29c199f3-63a8-3edb-b29e-de157431d89f@linux.ibm.com>
Date:   Mon, 19 Jul 2021 15:53:43 +0200
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On 16/07/2021 10:27, Leonardo Bras wrote:
> @@ -1099,18 +1105,13 @@ int iommu_take_ownership(struct iommu_table *tbl)
>   	for (i = 0; i < tbl->nr_pools; i++)
>   		spin_lock_nest_lock(&tbl->pools[i].lock, &tbl->large_pool.lock);
>   
> -	iommu_table_release_pages(tbl);
> -
> -	if (!bitmap_empty(tbl->it_map, tbl->it_size)) {
> +	if (iommu_table_in_use(tbl)) {
>   		pr_err("iommu_tce: it_map is not empty");
>   		ret = -EBUSY;
> -		/* Undo iommu_table_release_pages, i.e. restore bit#0, etc */
> -		iommu_table_reserve_pages(tbl, tbl->it_reserved_start,
> -				tbl->it_reserved_end);
> -	} else {
> -		memset(tbl->it_map, 0xff, sz);
>   	}
>   
> +	memset(tbl->it_map, 0xff, sz);
> +


So if the table is not empty, we fail (EBUSY) but we now also completely 
overwrite the bitmap. It was in an unexpected state, but we're making it 
worse. Or am I missing something?

   Fred


>   	for (i = 0; i < tbl->nr_pools; i++)
>   		spin_unlock(&tbl->pools[i].lock);
>   	spin_unlock_irqrestore(&tbl->large_pool.lock, flags);