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Message-ID: <3c75c46c-2a5a-cd75-83d4-f77d96d22f7d@oracle.com>
Date: Thu, 14 Feb 2019 09:56:24 -0700
From: Khalid Aziz <khalid.aziz@...cle.com>
To: Christoph Hellwig <hch@....de>
Cc: juergh@...il.com, tycho@...ho.ws, jsteckli@...zon.de, ak@...ux.intel.com,
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Tycho Andersen <tycho@...ker.com>
Subject: Re: [RFC PATCH v8 04/14] swiotlb: Map the buffer if it was unmapped
by XPFO
On 2/14/19 12:47 AM, Christoph Hellwig wrote:
> On Wed, Feb 13, 2019 at 05:01:27PM -0700, Khalid Aziz wrote:
>> +++ b/kernel/dma/swiotlb.c
>> @@ -396,8 +396,9 @@ static void swiotlb_bounce(phys_addr_t orig_addr, phys_addr_t tlb_addr,
>> {
>> unsigned long pfn = PFN_DOWN(orig_addr);
>> unsigned char *vaddr = phys_to_virt(tlb_addr);
>> + struct page *page = pfn_to_page(pfn);
>>
>> - if (PageHighMem(pfn_to_page(pfn))) {
>> + if (PageHighMem(page) || xpfo_page_is_unmapped(page)) {
>
> I think this just wants a page_unmapped or similar helper instead of
> needing the xpfo_page_is_unmapped check. We actually have quite
> a few similar construct in the arch dma mapping code for architectures
> that require cache flushing.
As I am not the original author of this patch, I am interpreting the
original intent. I think xpfo_page_is_unmapped() was added to account
for kernel build without CONFIG_XPFO. xpfo_page_is_unmapped() has an
alternate definition to return false if CONFIG_XPFO is not defined.
xpfo_is_unmapped() is cleaned up further in patch 11 ("xpfo, mm: remove
dependency on CONFIG_PAGE_EXTENSION") to a one-liner "return
PageXpfoUnmapped(page);". xpfo_is_unmapped() can be eliminated entirely
by adding an else clause to the following code added by that patch:
--- a/include/linux/page-flags.h
+++ b/include/linux/page-flags.h
@@ -398,6 +402,15 @@ TESTCLEARFLAG(Young, young, PF_ANY)
PAGEFLAG(Idle, idle, PF_ANY)
#endif
+#ifdef CONFIG_XPFO
+PAGEFLAG(XpfoUser, xpfo_user, PF_ANY)
+TESTCLEARFLAG(XpfoUser, xpfo_user, PF_ANY)
+TESTSETFLAG(XpfoUser, xpfo_user, PF_ANY)
+PAGEFLAG(XpfoUnmapped, xpfo_unmapped, PF_ANY)
+TESTCLEARFLAG(XpfoUnmapped, xpfo_unmapped, PF_ANY)
+TESTSETFLAG(XpfoUnmapped, xpfo_unmapped, PF_ANY)
+#endif
+
/*
* On an anonymous page mapped into a user virtual memory area,
* page->mapping points to its anon_vma, not to a struct address_space;
Adding the following #else to above conditional:
#else
TESTPAGEFLAG_FALSE(XpfoUser)
TESTPAGEFLAG_FALSE(XpfoUnmapped)
should allow us to eliminate xpfo_is_unmapped(). Right?
Thanks,
Khalid
>
>> +bool xpfo_page_is_unmapped(struct page *page)
>> +{
>> + struct xpfo *xpfo;
>> +
>> + if (!static_branch_unlikely(&xpfo_inited))
>> + return false;
>> +
>> + xpfo = lookup_xpfo(page);
>> + if (unlikely(!xpfo) && !xpfo->inited)
>> + return false;
>> +
>> + return test_bit(XPFO_PAGE_UNMAPPED, &xpfo->flags);
>> +}
>> +EXPORT_SYMBOL(xpfo_page_is_unmapped);
>
> And at least for swiotlb there is no need to export this helper,
> as it is always built in.
>
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