linux-kernel - Re: [Intel IOMMU 05/10] Intel IOMMU driver

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Date:	Tue, 19 Jun 2007 16:50:46 -0700
From:	"Keshavamurthy, Anil S" <anil.s.keshavamurthy@...el.com>
To:	Christoph Lameter <clameter@....com>
Cc:	"Keshavamurthy, Anil S" <anil.s.keshavamurthy@...el.com>,
	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	ak@...e.de, gregkh@...e.de, muli@...ibm.com,
	suresh.b.siddha@...el.com, arjan@...ux.intel.com,
	ashok.raj@...el.com, davem@...emloft.net
Subject: Re: [Intel IOMMU 05/10] Intel IOMMU driver

On Tue, Jun 19, 2007 at 04:32:23PM -0700, Christoph Lameter wrote:
> On Tue, 19 Jun 2007, Keshavamurthy, Anil S wrote:
> 
> > +static inline void *alloc_pgtable_page(void)
> > +{
> > +	return (void *)get_zeroed_page(GFP_ATOMIC);
> > +}
> 
> Need to pass gfp_t parameter. Repeates a couple of times.
> 
> > +	addr &= (((u64)1) << addr_width) - 1;
> > +	parent = domain->pgd;
> > +
> > +	spin_lock_irqsave(&domain->mapping_lock, flags);
> > +	while (level > 0) {
> > +		void *tmp_page;
> > +
> > +		offset = address_level_offset(addr, level);
> > +		pte = &parent[offset];
> > +		if (level == 1)
> > +			break;
> > +
> > +		if (!dma_pte_present(*pte)) {
> > +			tmp_page = alloc_pgtable_page();
> 
> Is it not possible here to drop the lock and do the alloc with GFP_KERNEL 
> and deal with the resulting race? That is done in other parts of the 
> kernel.
> 
> > +/* iommu handling */
> > +static int iommu_alloc_root_entry(struct intel_iommu *iommu)
> > +{
> > +	struct root_entry *root;
> > +	unsigned long flags;
> > +
> > +	root = (struct root_entry *)alloc_pgtable_page();
> 
> This may be able to become a GFP_KERNEL alloc since interrupts are enabled 
> at this point?

Memory allocated during driver init is very less and not much benefit
with the suggested changes I think. Please correct me If I am wrong.

The biggest benifit will be when we can figure out GPF_XXXX flags
during runtime when DMA map api's are called. 
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