Re: [PATCH 1/2] fs/dax: deposit pagetable even when installing zero page

Jan Kara
2019-02-28T09:21:06Z

On Thu 28-02-19 14:05:21, Aneesh Kumar K.V wrote:
> Architectures like ppc64 use the deposited page table to store hardware
> page table slot information. Make sure we deposit a page table when
> using zero page at the pmd level for hash.
>
> Without this we hit
>
> Unable to handle kernel paging request for data at address 0x00000000
> Faulting instruction address: 0xc000000000082a74
> Oops: Kernel access of bad area, sig: 11 [#1]
> ....
>
> NIP [c000000000082a74] __hash_page_thp+0x224/0x5b0
> LR [c0000000000829a4] __hash_page_thp+0x154/0x5b0
> Call Trace:
> hash_page_mm+0x43c/0x740
> do_hash_page+0x2c/0x3c
> copy_from_iter_flushcache+0xa4/0x4a0
> pmem_copy_from_iter+0x2c/0x50 [nd_pmem]
> dax_copy_from_iter+0x40/0x70
> dax_iomap_actor+0x134/0x360
> iomap_apply+0xfc/0x1b0
> dax_iomap_rw+0xac/0x130
> ext4_file_write_iter+0x254/0x460 [ext4]
> __vfs_write+0x120/0x1e0
> vfs_write+0xd8/0x220
> SyS_write+0x6c/0x110
> system_call+0x3c/0x130
>
> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>

Thanks for the patch. It looks good to me. You can add:

Reviewed-by: Jan Kara <jack@suse.cz>

> ---
> TODO:
> * Add fixes tag

Probably this is a problem since initial PPC PMEM support, isn't it?

Honza

>
> fs/dax.c | 15 +++++++++++++++
> 1 file changed, 15 insertions(+)
>
> diff --git a/fs/dax.c b/fs/dax.c
> index 6959837cc465..01bfb2ac34f9 100644
> --- a/fs/dax.c
> +++ b/fs/dax.c
> @@ -33,6 +33,7 @@
> #include <linux/sizes.h>
> #include <linux/mmu_notifier.h>
> #include <linux/iomap.h>
> +#include <asm/pgalloc.h>
> #include "internal.h"
>
> #define CREATE_TRACE_POINTS
> @@ -1410,7 +1411,9 @@ static vm_fault_t dax_pmd_load_hole(struct xa_state *xas, struct vm_fault *vmf,
> {
> struct address_space *mapping = vmf->vma->vm_file->f_mapping;
> unsigned long pmd_addr = vmf->address & PMD_MASK;
> + struct vm_area_struct *vma = vmf->vma;
> struct inode *inode = mapping->host;
> + pgtable_t pgtable = NULL;
> struct page *zero_page;
> spinlock_t *ptl;
> pmd_t pmd_entry;
> @@ -1425,12 +1428,22 @@ static vm_fault_t dax_pmd_load_hole(struct xa_state *xas, struct vm_fault *vmf,
> *entry = dax_insert_entry(xas, mapping, vmf, *entry, pfn,
> DAX_PMD | DAX_ZERO_PAGE, false);
>
> + if (arch_needs_pgtable_deposit()) {
> + pgtable = pte_alloc_one(vma->vm_mm);
> + if (!pgtable)
> + return VM_FAULT_OOM;
> + }
> +
> ptl = pmd_lock(vmf->vma->vm_mm, vmf->pmd);
> if (!pmd_none(*(vmf->pmd))) {
> spin_unlock(ptl);
> goto fallback;
> }
>
> + if (pgtable) {
> + pgtable_trans_huge_deposit(vma->vm_mm, vmf->pmd, pgtable);
> + mm_inc_nr_ptes(vma->vm_mm);
> + }
> pmd_entry = mk_pmd(zero_page, vmf->vma->vm_page_prot);
> pmd_entry = pmd_mkhuge(pmd_entry);
> set_pmd_at(vmf->vma->vm_mm, pmd_addr, vmf->pmd, pmd_entry);
> @@ -1439,6 +1452,8 @@ static vm_fault_t dax_pmd_load_hole(struct xa_state *xas, struct vm_fault *vmf,
> return VM_FAULT_NOPAGE;
>
> fallback:
> + if (pgtable)
> + pte_free(vma->vm_mm, pgtable);
> trace_dax_pmd_load_hole_fallback(inode, vmf, zero_page, *entry);
> return VM_FAULT_FALLBACK;
> }
> --
> 2.20.1
>
--
Jan Kara <jack@suse.com>
SUSE Labs, CR