linux-kernel - Re: [PATCH kernel v10 19/34] powerpc/iommu: Fix IOMMU ownership control functions

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Date:	Thu, 14 May 2015 13:36:55 +1000
From:	Gavin Shan <gwshan@...ux.vnet.ibm.com>
To:	Alexey Kardashevskiy <aik@...abs.ru>
Cc:	linuxppc-dev@...ts.ozlabs.org,
	David Gibson <david@...son.dropbear.id.au>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mackerras <paulus@...ba.org>,
	Alex Williamson <alex.williamson@...hat.com>,
	Gavin Shan <gwshan@...ux.vnet.ibm.com>,
	Wei Yang <weiyang@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH kernel v10 19/34] powerpc/iommu: Fix IOMMU ownership
 control functions

On Tue, May 12, 2015 at 01:39:08AM +1000, Alexey Kardashevskiy wrote:
>This adds missing locks in iommu_take_ownership()/
>iommu_release_ownership().
>
>This marks all pages busy in iommu_table::it_map in order to catch
>errors if there is an attempt to use this table while ownership over it
>is taken.
>
>This only clears TCE content if there is no page marked busy in it_map.
>Clearing must be done outside of the table locks as iommu_clear_tce()
>called from iommu_clear_tces_and_put_pages() does this.
>
>In order to use bitmap_empty(), the existing code clears bit#0 which
>is set even in an empty table if it is bus-mapped at 0 as
>iommu_init_table() reserves page#0 to prevent buggy drivers
>from crashing when allocated page is bus-mapped at zero
>(which is correct). This restores the bit in the case of failure
>to bring the it_map to the state it was in when we called
>iommu_take_ownership().
>
>Signed-off-by: Alexey Kardashevskiy <aik@...abs.ru>
>Reviewed-by: David Gibson <david@...son.dropbear.id.au>

Reviewed-by: Gavin Shan <gwshan@...ux.vnet.ibm.com>

Thanks,
Gavin

>---
>Changes:
>v9:
>* iommu_table_take_ownership() did not return @ret (and ignored EBUSY),
>now it does return correct error.
>* updated commit log about setting bit#0 in the case of failure
>
>v5:
>* do not store bit#0 value, it has to be set for zero-based table
>anyway
>* removed test_and_clear_bit
>---
> arch/powerpc/kernel/iommu.c | 30 +++++++++++++++++++++++++-----
> 1 file changed, 25 insertions(+), 5 deletions(-)
>
>diff --git a/arch/powerpc/kernel/iommu.c b/arch/powerpc/kernel/iommu.c
>index 7e54714..6275164 100644
>--- a/arch/powerpc/kernel/iommu.c
>+++ b/arch/powerpc/kernel/iommu.c
>@@ -1032,31 +1032,51 @@ EXPORT_SYMBOL_GPL(iommu_tce_build);
>
> int iommu_take_ownership(struct iommu_table *tbl)
> {
>-	unsigned long sz = (tbl->it_size + 7) >> 3;
>+	unsigned long flags, i, sz = (tbl->it_size + 7) >> 3;
>+	int ret = 0;
>+
>+	spin_lock_irqsave(&tbl->large_pool.lock, flags);
>+	for (i = 0; i < tbl->nr_pools; i++)
>+		spin_lock(&tbl->pools[i].lock);
>
> 	if (tbl->it_offset == 0)
> 		clear_bit(0, tbl->it_map);
>
> 	if (!bitmap_empty(tbl->it_map, tbl->it_size)) {
> 		pr_err("iommu_tce: it_map is not empty");
>-		return -EBUSY;
>+		ret = -EBUSY;
>+		/* Restore bit#0 set by iommu_init_table() */
>+		if (tbl->it_offset == 0)
>+			set_bit(0, tbl->it_map);
>+	} else {
>+		memset(tbl->it_map, 0xff, sz);
> 	}
>
>-	memset(tbl->it_map, 0xff, sz);
>+	for (i = 0; i < tbl->nr_pools; i++)
>+		spin_unlock(&tbl->pools[i].lock);
>+	spin_unlock_irqrestore(&tbl->large_pool.lock, flags);
>
>-	return 0;
>+	return ret;
> }
> EXPORT_SYMBOL_GPL(iommu_take_ownership);
>
> void iommu_release_ownership(struct iommu_table *tbl)
> {
>-	unsigned long sz = (tbl->it_size + 7) >> 3;
>+	unsigned long flags, i, sz = (tbl->it_size + 7) >> 3;
>+
>+	spin_lock_irqsave(&tbl->large_pool.lock, flags);
>+	for (i = 0; i < tbl->nr_pools; i++)
>+		spin_lock(&tbl->pools[i].lock);
>
> 	memset(tbl->it_map, 0, sz);
>
> 	/* Restore bit#0 set by iommu_init_table() */
> 	if (tbl->it_offset == 0)
> 		set_bit(0, tbl->it_map);
>+
>+	for (i = 0; i < tbl->nr_pools; i++)
>+		spin_unlock(&tbl->pools[i].lock);
>+	spin_unlock_irqrestore(&tbl->large_pool.lock, flags);
> }
> EXPORT_SYMBOL_GPL(iommu_release_ownership);
>
>-- 
>2.4.0.rc3.8.gfb3e7d5
>

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