[PATCH] powerpc/powernv: Fix vma page prot flags in opal-prd driver
opal-prd driver will mmap() firmware code/data area as private mapping to prd user space daemon. Write to this page will trigger COW faults. The new COW pages are normal kernel RAM pages accounted by the kernel and are not special. vma->vm_page_prot value will be used at page fault time for the new COW pages, while pgprot_t value passed in remap_pfn_range() is used for the initial page table entry. Hence: * Do not add _PAGE_SPECIAL in vma, but only for remap_pfn_range() * Also remap_pfn_range() will add the _PAGE_SPECIAL flag using pte_mkspecial() call, hence no need to specify in the driver This fix resolves the page accounting warning shown below: BUG: Bad rss-counter state mm:c007d34ac600 idx:1 val:19 The above warning is triggered since _PAGE_SPECIAL was incorrectly being set for the normal kernel COW pages. Signed-off-by: Vaidyanathan Srinivasan --- arch/powerpc/platforms/powernv/opal-prd.c |9 - 1 file changed, 4 insertions(+), 5 deletions(-) diff --git a/arch/powerpc/platforms/powernv/opal-prd.c b/arch/powerpc/platforms/powernv/opal-prd.c index 46cb3fe..4ece8e4 100644 --- a/arch/powerpc/platforms/powernv/opal-prd.c +++ b/arch/powerpc/platforms/powernv/opal-prd.c @@ -112,6 +112,7 @@ static int opal_prd_open(struct inode *inode, struct file *file) static int opal_prd_mmap(struct file *file, struct vm_area_struct *vma) { size_t addr, size; + pgprot_t page_prot; int rc; pr_devel("opal_prd_mmap(0x%016lx, 0x%016lx, 0x%lx, 0x%lx)\n", @@ -125,13 +126,11 @@ static int opal_prd_mmap(struct file *file, struct vm_area_struct *vma) if (!opal_prd_range_is_valid(addr, size)) return -EINVAL; - vma->vm_page_prot = __pgprot(pgprot_val(phys_mem_access_prot(file, - vma->vm_pgoff, -size, vma->vm_page_prot)) - | _PAGE_SPECIAL); + page_prot = phys_mem_access_prot(file, vma->vm_pgoff, +size, vma->vm_page_prot); rc = remap_pfn_range(vma, vma->vm_start, vma->vm_pgoff, size, - vma->vm_page_prot); + page_prot); return rc; } ___ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev
Re: [PATCH] powerpc/powernv: Fix vma page prot flags in opal-prd driver
* Vaidyanathan Srinivasan [2015-06-21 23:56:16]: > opal-prd driver will mmap() firmware code/data area as private > mapping to prd user space daemon. Write to this page will > trigger COW faults. The new COW pages are normal kernel RAM > pages accounted by the kernel and are not special. > > vma->vm_page_prot value will be used at page fault time > for the new COW pages, while pgprot_t value passed in > remap_pfn_range() is used for the initial page table entry. > > Hence: > * Do not add _PAGE_SPECIAL in vma, but only for remap_pfn_range() > * Also remap_pfn_range() will add the _PAGE_SPECIAL flag using > pte_mkspecial() call, hence no need to specify in the driver > > This fix resolves the page accounting warning shown below: > BUG: Bad rss-counter state mm:c007d34ac600 idx:1 val:19 > > The above warning is triggered since _PAGE_SPECIAL was incorrectly > being set for the normal kernel COW pages. > > Signed-off-by: Vaidyanathan Srinivasan > --- > arch/powerpc/platforms/powernv/opal-prd.c |9 - > 1 file changed, 4 insertions(+), 5 deletions(-) > > diff --git a/arch/powerpc/platforms/powernv/opal-prd.c > b/arch/powerpc/platforms/powernv/opal-prd.c > index 46cb3fe..4ece8e4 100644 > --- a/arch/powerpc/platforms/powernv/opal-prd.c > +++ b/arch/powerpc/platforms/powernv/opal-prd.c > @@ -112,6 +112,7 @@ static int opal_prd_open(struct inode *inode, struct file > *file) > static int opal_prd_mmap(struct file *file, struct vm_area_struct *vma) > { > size_t addr, size; > + pgprot_t page_prot; > int rc; > > pr_devel("opal_prd_mmap(0x%016lx, 0x%016lx, 0x%lx, 0x%lx)\n", > @@ -125,13 +126,11 @@ static int opal_prd_mmap(struct file *file, struct > vm_area_struct *vma) > if (!opal_prd_range_is_valid(addr, size)) > return -EINVAL; > > - vma->vm_page_prot = __pgprot(pgprot_val(phys_mem_access_prot(file, > - vma->vm_pgoff, > - size, vma->vm_page_prot)) > - | _PAGE_SPECIAL); > + page_prot = phys_mem_access_prot(file, vma->vm_pgoff, > + size, vma->vm_page_prot); > > rc = remap_pfn_range(vma, vma->vm_start, vma->vm_pgoff, size, > - vma->vm_page_prot); > + page_prot); Hi Ben, remap_pfn_range() is the correct method to map the firmware pages because we will not have struct page associated with this RAM area. We do a memblock_reserve() in early boot and take out this memory from kernel and avoid struct page allocation/init for these. vm_insert_page() is an alternative that would have worked if kernel allocated the memory, in which case we can bump up the page count and map the page to user space. This is already done by vm_insert_page() and we will not need to make the page special. However, this use case fits remap_pfn_range() and page special mechanism since there is no struct page associate with this physical pages. --Vaidy ___ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev
Re: [PATCH] powerpc/powernv: Fix vma page prot flags in opal-prd driver
* Vaidyanathan Srinivasan [2015-06-25 11:45:46]: [snip] > Hi Ben, > > remap_pfn_range() is the correct method to map the firmware pages > because we will not have struct page associated with this RAM area. > > We do a memblock_reserve() in early boot and take out this memory from > kernel and avoid struct page allocation/init for these. Kindly ignore the this comment. memblock_reserve() does not prevent/avoid struct page allocation. We do have valid struct page which can be used for mapping. --Vaidy ___ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev
[RESEND PATCH] powerpc/powernv: Fix vma page prot flags in opal-prd driver
opal-prd driver will mmap() firmware code/data area as private mapping to prd user space daemon. Write to this page will trigger COW faults. The new COW pages are normal kernel RAM pages accounted by the kernel and are not special. vma->vm_page_prot value will be used at page fault time for the new COW pages, while pgprot_t value passed in remap_pfn_range() is used for the initial page table entry. Hence: * Do not add _PAGE_SPECIAL in vma, but only for remap_pfn_range() * Also remap_pfn_range() will add the _PAGE_SPECIAL flag using pte_mkspecial() call, hence no need to specify in the driver This fix resolves the page accounting warning shown below: BUG: Bad rss-counter state mm:c007d34ac600 idx:1 val:19 The above warning is triggered since _PAGE_SPECIAL was incorrectly being set for the normal kernel COW pages. Signed-off-by: Vaidyanathan Srinivasan --- arch/powerpc/platforms/powernv/opal-prd.c |9 - 1 file changed, 4 insertions(+), 5 deletions(-) Resending the patch for inclusion until we have a working solution without PAGE_SPECIAL. Kindly queue this patch to fix the mmap issue in opal-prd driver. The next version/fix with vm_insert_page() will replace this code. There is no API change on the driver side and hence no side effects of including this fix until a better solution is available. diff --git a/arch/powerpc/platforms/powernv/opal-prd.c b/arch/powerpc/platforms/powernv/opal-prd.c index 46cb3fe..4ece8e4 100644 --- a/arch/powerpc/platforms/powernv/opal-prd.c +++ b/arch/powerpc/platforms/powernv/opal-prd.c @@ -112,6 +112,7 @@ static int opal_prd_open(struct inode *inode, struct file *file) static int opal_prd_mmap(struct file *file, struct vm_area_struct *vma) { size_t addr, size; + pgprot_t page_prot; int rc; pr_devel("opal_prd_mmap(0x%016lx, 0x%016lx, 0x%lx, 0x%lx)\n", @@ -125,13 +126,11 @@ static int opal_prd_mmap(struct file *file, struct vm_area_struct *vma) if (!opal_prd_range_is_valid(addr, size)) return -EINVAL; - vma->vm_page_prot = __pgprot(pgprot_val(phys_mem_access_prot(file, - vma->vm_pgoff, -size, vma->vm_page_prot)) - | _PAGE_SPECIAL); + page_prot = phys_mem_access_prot(file, vma->vm_pgoff, +size, vma->vm_page_prot); rc = remap_pfn_range(vma, vma->vm_start, vma->vm_pgoff, size, - vma->vm_page_prot); + page_prot); return rc; } ___ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev
Re: [RESEND PATCH] powerpc/powernv: Fix vma page prot flags in opal-prd driver
Hi Vaidy, > opal-prd driver will mmap() firmware code/data area as private > mapping to prd user space daemon. Write to this page will > trigger COW faults. The new COW pages are normal kernel RAM > pages accounted by the kernel and are not special. > > vma->vm_page_prot value will be used at page fault time > for the new COW pages, while pgprot_t value passed in > remap_pfn_range() is used for the initial page table entry. > > Hence: > * Do not add _PAGE_SPECIAL in vma, but only for remap_pfn_range() > * Also remap_pfn_range() will add the _PAGE_SPECIAL flag using > pte_mkspecial() call, hence no need to specify in the driver > > This fix resolves the page accounting warning shown below: > BUG: Bad rss-counter state mm:c007d34ac600 idx:1 val:19 > > The above warning is triggered since _PAGE_SPECIAL was incorrectly > being set for the normal kernel COW pages. > > Signed-off-by: Vaidyanathan Srinivasan Acked-by: Jeremy Kerr Cheers, Jeremy ___ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev