From: Joerg Roedel <[email protected]>
With huge-page ioremap areas the unmappings also need to be
synced between all page-tables. Otherwise it can cause data
corruption when a region is unmapped and later re-used.
Make the vmalloc_sync_one() function ready to sync
unmappings.
Fixes: 5d72b4fba40ef ('x86, mm: support huge I/O mapping capability I/F')
Signed-off-by: Joerg Roedel <[email protected]>
---
arch/x86/mm/fault.c | 7 ++++---
1 file changed, 4 insertions(+), 3 deletions(-)
diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index 4a4049f6d458..d71e167662c3 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -194,11 +194,12 @@ static inline pmd_t *vmalloc_sync_one(pgd_t *pgd, unsigned long address)
pmd = pmd_offset(pud, address);
pmd_k = pmd_offset(pud_k, address);
- if (!pmd_present(*pmd_k))
- return NULL;
- if (!pmd_present(*pmd))
+ if (pmd_present(*pmd) ^ pmd_present(*pmd_k))
set_pmd(pmd, *pmd_k);
+
+ if (!pmd_present(*pmd_k))
+ return NULL;
else
BUG_ON(pmd_pfn(*pmd) != pmd_pfn(*pmd_k));
--
2.17.1
On 7/17/19 12:14 AM, Joerg Roedel wrote:
>
> diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
> index 4a4049f6d458..d71e167662c3 100644
> --- a/arch/x86/mm/fault.c
> +++ b/arch/x86/mm/fault.c
> @@ -194,11 +194,12 @@ static inline pmd_t *vmalloc_sync_one(pgd_t *pgd, unsigned long address)
>
> pmd = pmd_offset(pud, address);
> pmd_k = pmd_offset(pud_k, address);
> - if (!pmd_present(*pmd_k))
> - return NULL;
>
> - if (!pmd_present(*pmd))
> + if (pmd_present(*pmd) ^ pmd_present(*pmd_k))
> set_pmd(pmd, *pmd_k);
Wouldn't:
if (pmd_present(*pmd) != pmd_present(*pmd_k))
set_pmd(pmd, *pmd_k);
be a bit more intuitive?
But, either way, these look fine. For the series:
Reviewed-by: Dave Hansen <[email protected]>
On Wed, 17 Jul 2019, Joerg Roedel wrote:
> From: Joerg Roedel <[email protected]>
>
> With huge-page ioremap areas the unmappings also need to be
> synced between all page-tables. Otherwise it can cause data
> corruption when a region is unmapped and later re-used.
>
> Make the vmalloc_sync_one() function ready to sync
> unmappings.
>
> Fixes: 5d72b4fba40ef ('x86, mm: support huge I/O mapping capability I/F')
> Signed-off-by: Joerg Roedel <[email protected]>
> ---
> arch/x86/mm/fault.c | 7 ++++---
> 1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
> index 4a4049f6d458..d71e167662c3 100644
> --- a/arch/x86/mm/fault.c
> +++ b/arch/x86/mm/fault.c
> @@ -194,11 +194,12 @@ static inline pmd_t *vmalloc_sync_one(pgd_t *pgd, unsigned long address)
>
> pmd = pmd_offset(pud, address);
> pmd_k = pmd_offset(pud_k, address);
> - if (!pmd_present(*pmd_k))
> - return NULL;
>
> - if (!pmd_present(*pmd))
> + if (pmd_present(*pmd) ^ pmd_present(*pmd_k))
> set_pmd(pmd, *pmd_k);
> +
> + if (!pmd_present(*pmd_k))
> + return NULL;
> else
> BUG_ON(pmd_pfn(*pmd) != pmd_pfn(*pmd_k));
So in case of unmap, this updates only the first entry in the pgd_list
because vmalloc_sync_all() will break out of the iteration over pgd_list
when NULL is returned from vmalloc_sync_one().
I'm surely missing something, but how is that supposed to sync _all_ page
tables on unmap as the changelog claims?
Thanks,
tglx
Hi Dave,
On Wed, Jul 17, 2019 at 02:06:01PM -0700, Dave Hansen wrote:
> On 7/17/19 12:14 AM, Joerg Roedel wrote:
> > - if (!pmd_present(*pmd))
> > + if (pmd_present(*pmd) ^ pmd_present(*pmd_k))
> > set_pmd(pmd, *pmd_k);
>
> Wouldn't:
>
> if (pmd_present(*pmd) != pmd_present(*pmd_k))
> set_pmd(pmd, *pmd_k);
>
> be a bit more intuitive?
Yes, right. That is much better, I changed it in the patch.
> But, either way, these look fine. For the series:
>
> Reviewed-by: Dave Hansen <[email protected]>
Thanks!
Joerg
Hi Thomas,
On Wed, Jul 17, 2019 at 11:43:43PM +0200, Thomas Gleixner wrote:
> On Wed, 17 Jul 2019, Joerg Roedel wrote:
> > +
> > + if (!pmd_present(*pmd_k))
> > + return NULL;
> > else
> > BUG_ON(pmd_pfn(*pmd) != pmd_pfn(*pmd_k));
>
> So in case of unmap, this updates only the first entry in the pgd_list
> because vmalloc_sync_all() will break out of the iteration over pgd_list
> when NULL is returned from vmalloc_sync_one().
>
> I'm surely missing something, but how is that supposed to sync _all_ page
> tables on unmap as the changelog claims?
No, you are right, I missed that. It is a bug in this patch, the code
that breaks out of the loop in vmalloc_sync_all() needs to be removed as
well. Will do that in the next version.
Thanks,
Joerg
Joerg,
On Thu, 18 Jul 2019, Joerg Roedel wrote:
> On Wed, Jul 17, 2019 at 11:43:43PM +0200, Thomas Gleixner wrote:
> > On Wed, 17 Jul 2019, Joerg Roedel wrote:
> > > +
> > > + if (!pmd_present(*pmd_k))
> > > + return NULL;
> > > else
> > > BUG_ON(pmd_pfn(*pmd) != pmd_pfn(*pmd_k));
> >
> > So in case of unmap, this updates only the first entry in the pgd_list
> > because vmalloc_sync_all() will break out of the iteration over pgd_list
> > when NULL is returned from vmalloc_sync_one().
> >
> > I'm surely missing something, but how is that supposed to sync _all_ page
> > tables on unmap as the changelog claims?
>
> No, you are right, I missed that. It is a bug in this patch, the code
> that breaks out of the loop in vmalloc_sync_all() needs to be removed as
> well. Will do that in the next version.
I assume that p4d/pud do not need the pmd treatment, but a comment
explaining why would be appreciated.
Thanks,
tglx
On Thu, Jul 18, 2019 at 11:04:57AM +0200, Thomas Gleixner wrote:
> On Thu, 18 Jul 2019, Joerg Roedel wrote:
> > No, you are right, I missed that. It is a bug in this patch, the code
> > that breaks out of the loop in vmalloc_sync_all() needs to be removed as
> > well. Will do that in the next version.
>
> I assume that p4d/pud do not need the pmd treatment, but a comment
> explaining why would be appreciated.
Yes, p4d and pud don't need to be handled here, as the code is 32-bit
only and there p4d is folded anyway. Pud is only relevant for PAE and
will already be mapped when the page-table is created (for performance
reasons, because pud is top-level at PAE and mapping it later requires a
TLB flush).
The pud with PAE also never changes during the life-time of the
page-table because we can't map a huge-page there. I will put that into
a comment.
Thanks,
Joerg
On Thu, Jul 18, 2019 at 11:04:57AM +0200, Thomas Gleixner wrote:
> Joerg,
>
> On Thu, 18 Jul 2019, Joerg Roedel wrote:
> > On Wed, Jul 17, 2019 at 11:43:43PM +0200, Thomas Gleixner wrote:
> > > On Wed, 17 Jul 2019, Joerg Roedel wrote:
> > > > +
> > > > + if (!pmd_present(*pmd_k))
> > > > + return NULL;
> > > > else
> > > > BUG_ON(pmd_pfn(*pmd) != pmd_pfn(*pmd_k));
> > >
> > > So in case of unmap, this updates only the first entry in the pgd_list
> > > because vmalloc_sync_all() will break out of the iteration over pgd_list
> > > when NULL is returned from vmalloc_sync_one().
> > >
> > > I'm surely missing something, but how is that supposed to sync _all_ page
> > > tables on unmap as the changelog claims?
> >
> > No, you are right, I missed that. It is a bug in this patch, the code
> > that breaks out of the loop in vmalloc_sync_all() needs to be removed as
> > well. Will do that in the next version.
>
> I assume that p4d/pud do not need the pmd treatment, but a comment
> explaining why would be appreciated.
Actually there is already a comment in this function explaining why p4d
and pud don't need any treatment:
/*
* set_pgd(pgd, *pgd_k); here would be useless on PAE
* and redundant with the set_pmd() on non-PAE. As would
* set_p4d/set_pud.
*/
I couldn't say it with less words :)
Regards,
Joerg
On Fri, 19 Jul 2019, Joerg Roedel wrote:
> On Thu, Jul 18, 2019 at 11:04:57AM +0200, Thomas Gleixner wrote:
> > Joerg,
> >
> > On Thu, 18 Jul 2019, Joerg Roedel wrote:
> > > On Wed, Jul 17, 2019 at 11:43:43PM +0200, Thomas Gleixner wrote:
> > > > On Wed, 17 Jul 2019, Joerg Roedel wrote:
> > > > > +
> > > > > + if (!pmd_present(*pmd_k))
> > > > > + return NULL;
> > > > > else
> > > > > BUG_ON(pmd_pfn(*pmd) != pmd_pfn(*pmd_k));
> > > >
> > > > So in case of unmap, this updates only the first entry in the pgd_list
> > > > because vmalloc_sync_all() will break out of the iteration over pgd_list
> > > > when NULL is returned from vmalloc_sync_one().
> > > >
> > > > I'm surely missing something, but how is that supposed to sync _all_ page
> > > > tables on unmap as the changelog claims?
> > >
> > > No, you are right, I missed that. It is a bug in this patch, the code
> > > that breaks out of the loop in vmalloc_sync_all() needs to be removed as
> > > well. Will do that in the next version.
> >
> > I assume that p4d/pud do not need the pmd treatment, but a comment
> > explaining why would be appreciated.
>
> Actually there is already a comment in this function explaining why p4d
> and pud don't need any treatment:
>
> /*
> * set_pgd(pgd, *pgd_k); here would be useless on PAE
> * and redundant with the set_pmd() on non-PAE. As would
> * set_p4d/set_pud.
> */
Indeed. Why did I think there was none?
> I couldn't say it with less words :)
It's perfectly fine.
Thanks,
tglx