linux-kernel - Re: [PATCH] intel-iommu: Manage iommu

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Date:	Fri, 18 Nov 2011 18:15:17 +0000
From:	David Woodhouse <dwmw2@...radead.org>
To:	Alex Williamson <alex.williamson@...hat.com>
Cc:	rajesh.sankaran@...el.com, iommu@...ts.linux-foundation.org,
	linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
	chrisw@...s-sol.org, ddutile@...hat.com
Subject: Re: [PATCH] intel-iommu: Manage iommu_coherency globally

On Fri, 2011-11-18 at 10:15 -0700, Alex Williamson wrote:
> A bit heavy handed, but obviously easier.  It feels like we could safely
> be more strategic, but maybe we'd end up trashing the cache anyway in a
> drawn out attempt to flush the context and all page tables.  However, do
> we actually need a wbinvd_on_all_cpus()?  Probably better to trash one
> cache than all of them.  Thanks, 

Yes, it would be wbinvd_on_all_cpus(). The page-table-walk code would
look something like this...

static void flush_domain_ptes(struct dmar_domain *domain)
{
	int level = agaw_to_level(domain->agaw);
	struct dma_pte *ptelvl[level + 2], *pte;

	pte = domain->pgd;
	clflush_cache_range(pte, VTD_PAGE_SIZE);

	/* Keep the end condition nice and simple... */
	ptelvl[level + 1] = NULL;

	while (pte) {
		/* BUG_ON(level < 2); */
		if (dma_pte_present(pte)) {
			if (level == 2) {
				/* Flush the bottom-level page, but no need to
				   process its *contents* any further. */
				clflush_cache_range(phys_to_virt(dma_pte_addr(pte)),
						    VTD_PAGE_SIZE);
			} else if (!(pte->val & DMA_PTE_LARGE_PAGE)) {
				/* Remember the next PTE at this level; we'll
				   come back to it. */
				ptelvl[level] = pte + 1;

				/* Go down a level and process PTEs there. */
				pte = phys_to_virt(dma_pte_addr(pte));
				clflush_cache_range(pte, VTD_PAGE_SIZE);
				level--;
				continue;
			}
		}
		
		pte++;
		/* When we reach the end of a PTE page, go back up to the next
		   level where we came from. */
		while (pte && !((unsigned long)pte & ~VTD_PAGE_MASK)) {
			level++;
			pte = ptelvl[level];
		}
	}
}

-- 
dwmw2

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