From: Mike Kravetz <mike.kravetz@oracle.com>
To: "Axel Rasmussen" <axelrasmussen@google.com>,
"Alexander Viro" <viro@zeniv.linux.org.uk>,
"Alexey Dobriyan" <adobriyan@gmail.com>,
"Andrea Arcangeli" <aarcange@redhat.com>,
"Andrew Morton" <akpm@linux-foundation.org>,
"Anshuman Khandual" <anshuman.khandual@arm.com>,
"Catalin Marinas" <catalin.marinas@arm.com>,
"Chinwen Chang" <chinwen.chang@mediatek.com>,
"Huang Ying" <ying.huang@intel.com>,
"Ingo Molnar" <mingo@redhat.com>, "Jann Horn" <jannh@google.com>,
"Jerome Glisse" <jglisse@redhat.com>,
"Lokesh Gidra" <lokeshgidra@google.com>,
"Matthew Wilcox (Oracle)" <willy@infradead.org>,
"Michael Ellerman" <mpe@ellerman.id.au>,
"Michal Koutný" <mkoutny@suse.com>,
"Michel Lespinasse" <walken@google.com>,
"Mike Rapoport" <rppt@linux.vnet.ibm.com>,
"Nicholas Piggin" <npiggin@gmail.com>,
"Peter Xu" <peterx@redhat.com>, "Shaohua Li" <shli@fb.com>,
"Shawn Anastasio" <shawn@anastas.io>,
"Steven Rostedt" <rostedt@goodmis.org>,
"Steven Price" <steven.price@arm.com>,
"Vlastimil Babka" <vbabka@suse.cz>
Cc: linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
linux-mm@kvack.org, Adam Ruprecht <ruprecht@google.com>,
Cannon Matthews <cannonmatthews@google.com>,
"Dr . David Alan Gilbert" <dgilbert@redhat.com>,
David Rientjes <rientjes@google.com>,
Mina Almasry <almasrymina@google.com>,
Oliver Upton <oupton@google.com>
Subject: Re: [PATCH v7 1/6] userfaultfd: add minor fault registration mode
Date: Wed, 24 Feb 2021 16:24:58 -0800 [thread overview]
Message-ID: <6aefd704-f720-35dc-d71c-da9840dc93a6@oracle.com> (raw)
In-Reply-To: <20210219004824.2899045-2-axelrasmussen@google.com>
On 2/18/21 4:48 PM, Axel Rasmussen wrote:
<snip>
> @@ -401,8 +398,10 @@ vm_fault_t handle_userfault(struct vm_fault *vmf, unsigned long reason)
>
> BUG_ON(ctx->mm != mm);
>
> - VM_BUG_ON(reason & ~(VM_UFFD_MISSING|VM_UFFD_WP));
> - VM_BUG_ON(!(reason & VM_UFFD_MISSING) ^ !!(reason & VM_UFFD_WP));
> + /* Any unrecognized flag is a bug. */
> + VM_BUG_ON(reason & ~__VM_UFFD_FLAGS);
> + /* 0 or > 1 flags set is a bug; we expect exactly 1. */
> + VM_BUG_ON(!reason || !!(reason & (reason - 1)));
I may be confused, but that seems to be checking for a flag value of 1
as opposed to one flag being set?
>
> if (ctx->features & UFFD_FEATURE_SIGBUS)
> goto out;
<snip>
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 3bfba75f6cbd..0388107da4b1 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -4352,6 +4352,38 @@ static vm_fault_t hugetlb_no_page(struct mm_struct *mm,
> VM_FAULT_SET_HINDEX(hstate_index(h));
> goto backout_unlocked;
> }
> +
> + /* Check for page in userfault range. */
> + if (userfaultfd_minor(vma)) {
> + u32 hash;
> + struct vm_fault vmf = {
> + .vma = vma,
> + .address = haddr,
> + .flags = flags,
> + /*
> + * Hard to debug if it ends up being used by a
> + * callee that assumes something about the
> + * other uninitialized fields... same as in
> + * memory.c
> + */
> + };
> +
> + unlock_page(page);
> +
> + /*
> + * hugetlb_fault_mutex and i_mmap_rwsem must be dropped
> + * before handling userfault. Reacquire after handling
> + * fault to make calling code simpler.
> + */
> +
> + hash = hugetlb_fault_mutex_hash(mapping, idx);
> + mutex_unlock(&hugetlb_fault_mutex_table[hash]);
> + i_mmap_unlock_read(mapping);
> + ret = handle_userfault(&vmf, VM_UFFD_MINOR);
> + i_mmap_lock_read(mapping);
> + mutex_lock(&hugetlb_fault_mutex_table[hash]);
> + goto out;
> + }
> }
>
> /*
>
I'm good with the hugetlb.c changes. Since this in nearly identical to
the other handle_userfault() in this routine, it might be good to create
a common wrapper. But, that is not required.
--
Mike Kravetz
next prev parent reply other threads:[~2021-02-25 0:26 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-19 0:48 [PATCH v7 0/6] userfaultfd: add minor fault handling Axel Rasmussen
2021-02-19 0:48 ` [PATCH v7 1/6] userfaultfd: add minor fault registration mode Axel Rasmussen
2021-02-23 15:20 ` Peter Xu
2021-02-25 0:24 ` Mike Kravetz [this message]
2021-02-25 17:49 ` Axel Rasmussen
2021-02-25 18:48 ` Mike Kravetz
2021-02-19 0:48 ` [PATCH v7 2/6] userfaultfd: disable huge PMD sharing for MINOR registered VMAs Axel Rasmussen
2021-02-25 0:33 ` Mike Kravetz
2021-02-19 0:48 ` [PATCH v7 3/6] userfaultfd: hugetlbfs: only compile UFFD helpers if config enabled Axel Rasmussen
2021-02-19 0:48 ` [PATCH v7 4/6] userfaultfd: add UFFDIO_CONTINUE ioctl Axel Rasmussen
2021-02-23 15:38 ` Peter Xu
2021-02-23 18:05 ` Axel Rasmussen
2021-02-23 18:28 ` Peter Xu
2021-02-19 0:48 ` [PATCH v7 5/6] userfaultfd: update documentation to describe minor fault handling Axel Rasmussen
2021-02-19 0:48 ` [PATCH v7 6/6] userfaultfd/selftests: add test exercising " Axel Rasmussen
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