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Message-id: <20130809173357.841dad5f7a648604f597c18d@samsung.com>
Date: Fri, 09 Aug 2013 17:33:57 +0900
From: Cho KyongHo <pullip.cho@...sung.com>
To: Tomasz Figa <tomasz.figa@...il.com>
Cc: Tomasz Figa <t.figa@...sung.com>,
'Linux ARM Kernel' <linux-arm-kernel@...ts.infradead.org>,
'Linux IOMMU' <iommu@...ts.linux-foundation.org>,
'Linux Kernel' <linux-kernel@...r.kernel.org>,
'Linux Samsung SOC' <linux-samsung-soc@...r.kernel.org>,
devicetree@...r.kernel.org, 'Joerg Roedel' <joro@...tes.org>,
'Kukjin Kim' <kgene.kim@...sung.com>,
'Prathyush' <prathyush.k@...sung.com>,
'Rahul Sharma' <rahul.sharma@...sung.com>,
'Subash Patel' <supash.ramaswamy@...aro.org>,
'Grant Grundler' <grundler@...omium.org>,
'Antonios Motakis' <a.motakis@...tualopensystems.com>,
kvmarm@...ts.cs.columbia.edu,
'Sachin Kamat' <sachin.kamat@...aro.org>
Subject: Re: [PATCH v9 03/16] iommu/exynos: fix page table maintenance
On Fri, 09 Aug 2013 09:47:28 +0200, Tomasz Figa wrote:
> Hi KyongHo,
>
> On Friday 09 of August 2013 13:15:20 Cho KyongHo wrote:
> > On Thu, 08 Aug 2013 15:54:50 +0200, Tomasz Figa wrote:
> > > On Thursday 08 of August 2013 18:37:43 Cho KyongHo wrote:
> > > > This prevents allocating lv2 page table for the lv1 page table entry
> > > >
> > > ^ What this is this this about? :)
> >
> > As you might indicate, 'this' means this patch :)
>
> Yep, I was just nitpicking, but still I would go with something among
> following lines:
>
> 8<---
> Currently if lv2 page table allocation is requested for a lv1 page table
> entry that already has 1MB page mapping, the driver returns -EADDRINUSE.
> However this case should not happen, unless there is a bug in the generic
> IOMMU allocator, so BUG_ON() is the right error handling here, which is
> implemented by this patch.
> --->8
>
> > > > that already has 1MB page mapping. In addition, changed to BUG_ON
> > > > instead of returning -EADDRINUSE.
> > >
> > > The change mentioned in last sentence should be a separate patch.
> >
> > Ok :)
>
> Well, actually I was confused by subject of this patch.
>
> It looks like this change is actually the main part of it and the only
> unrelated changes are using defined macros for page masks and introduction
> of clear_page_table() function. Since we both agreed that the latter can
> be dropped only the former should be separated from this patch.
>
> Maybe you could use following patch subject:
>
> iommu/exynos: fix handling of possible BUG cases in page table setup code
>
Your title looks much better. Thanks.
Initially, this patch is created for handling -EADDRINUSE correctly but
it is changed :). I missed to change the subject.
> > > > Signed-off-by: Cho KyongHo <pullip.cho@...sung.com>
> > > > ---
> > > >
> > > > drivers/iommu/exynos-iommu.c | 68
> > > >
> > > > ++++++++++++++++++++++++----------------- 1 files changed, 40
> > > > insertions(+), 28 deletions(-)
> > > >
> > > > diff --git a/drivers/iommu/exynos-iommu.c
> > > > b/drivers/iommu/exynos-iommu.c index d545a25..d90e6fa 100644
> > > > --- a/drivers/iommu/exynos-iommu.c
> > > > +++ b/drivers/iommu/exynos-iommu.c
> > > > @@ -52,11 +52,11 @@
> > > >
> > > > #define lv2ent_large(pent) ((*(pent) & 3) == 1)
> > > >
> > > > #define section_phys(sent) (*(sent) & SECT_MASK)
> > > >
> > > > -#define section_offs(iova) ((iova) & 0xFFFFF)
> > > > +#define section_offs(iova) ((iova) & ~SECT_MASK)
> > > >
> > > > #define lpage_phys(pent) (*(pent) & LPAGE_MASK)
> > > >
> > > > -#define lpage_offs(iova) ((iova) & 0xFFFF)
> > > > +#define lpage_offs(iova) ((iova) & ~LPAGE_MASK)
> > > >
> > > > #define spage_phys(pent) (*(pent) & SPAGE_MASK)
> > > >
> > > > -#define spage_offs(iova) ((iova) & 0xFFF)
> > > > +#define spage_offs(iova) ((iova) & ~SPAGE_MASK)
> > > >
> > > > #define lv1ent_offset(iova) ((iova) >> SECT_ORDER)
> > > > #define lv2ent_offset(iova) (((iova) & 0xFF000) >> SPAGE_ORDER)
> > > >
> > > > @@ -856,13 +856,15 @@ finish:
> > > > static unsigned long *alloc_lv2entry(unsigned long *sent, unsigned
> > > > long
> > > >
> > > > iova, short *pgcounter)
> > > >
> > > > {
> > > >
> > > > + BUG_ON(lv1ent_section(sent));
> > >
> > > Is this condition really a critical one, to the point that the system
> > > should not continue execution?
> >
> > Discussed with Grant. He thought that creating mapping on a valid
> > mapping is just a BUG and I finally agreed with him. Is there a case
> > that the condition in BUG_ON is true intentionally?
>
> Yes, he explained this as well. It's fine for me then.
>
> > > > +
> > > >
> > > > if (lv1ent_fault(sent)) {
> > > >
> > > > unsigned long *pent;
> > > >
> > > > pent = kzalloc(LV2TABLE_SIZE, GFP_ATOMIC);
> > > > BUG_ON((unsigned long)pent & (LV2TABLE_SIZE - 1));
> > > > if (!pent)
> > > >
> > > > - return NULL;
> > > > + return ERR_PTR(-ENOMEM);
> > > >
> > > > *sent = mk_lv1ent_page(__pa(pent));
> > > > *pgcounter = NUM_LV2ENTRIES;
> > > >
> > > > @@ -875,15 +877,11 @@ static unsigned long *alloc_lv2entry(unsigned
> > > > long *sent, unsigned long iova,
> > > >
> > > > static int lv1set_section(unsigned long *sent, phys_addr_t paddr,
> > > > short
> > > >
> > > > *pgcnt) {
> > > > - if (lv1ent_section(sent))
> > > > - return -EADDRINUSE;
> > > > + BUG_ON(lv1ent_section(sent));
> > >
> > > Ditto.
> > >
> > > > if (lv1ent_page(sent)) {
> > > >
> > > > - if (*pgcnt != NUM_LV2ENTRIES)
> > > > - return -EADDRINUSE;
> > > > -
> > > > + BUG_ON(*pgcnt != NUM_LV2ENTRIES);
> > >
> > > Ditto.
> > >
> > > > kfree(page_entry(sent, 0));
> > > >
> > > > -
> > > >
> > > > *pgcnt = 0;
> > > >
> > > > }
> > > >
> > > > @@ -894,24 +892,24 @@ static int lv1set_section(unsigned long *sent,
> > > > phys_addr_t paddr, short *pgcnt) return 0;
> > > >
> > > > }
> > > >
> > > > +static void clear_page_table(unsigned long *ent, int n)
> > > > +{
> > > > + if (n > 0)
> > > > + memset(ent, 0, sizeof(*ent) * n);
> > > > +}
> > >
> > > I don't see the point of creating this function. It seems to be used
> > > only once, in addition with a constant as n, so the check for n > 0
> > > is unnecessary.
> > >
> > > And even if there is a need for this change, it should be done in
> > > separate patch, as this one is not about stylistic changes, but
> > > fixing page table maintenance (at least based on your commit
> > > message).
> >
> > I know what you are concerning about.
> > It was introduced in v8 patches to recover previous fault entries before
> > returning -EADDRINUSE. It is still remained though "return -EADDRINUSE"
> > is changed into BUG_ON().
> > I also think that it needs to be removed.
>
> OK, thanks.
>
> Best regards,
> Tomasz
>
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