From: Paolo Bonzini <pbonzini@redhat.com>
To: Christoph Hellwig <hch@infradead.org>
Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org, jgg@ziepe.ca,
linux-mm@kvack.org, Andrew Morton <akpm@linux-foundation.org>,
dan.j.williams@intel.com
Subject: Re: [PATCH 1/2] mm: provide a sane PTE walking API for modules
Date: Mon, 8 Feb 2021 19:18:56 +0100 [thread overview]
Message-ID: <3b10057c-e117-89fa-1bd4-23fb5a4efb5f@redhat.com> (raw)
In-Reply-To: <20210208173936.GA1496438@infradead.org>
On 08/02/21 18:39, Christoph Hellwig wrote:
>> +int follow_pte(struct mm_struct *mm, unsigned long address,
>> + pte_t **ptepp, spinlock_t **ptlp)
>> +{
>> + return follow_invalidate_pte(mm, address, NULL, ptepp, NULL, ptlp);
>> +}
>> +EXPORT_SYMBOL_GPL(follow_pte);
>
> I still don't think this is good as a general API. Please document this
> as KVM only for now, and hopefully next merge window I'll finish an
> export variant restricting us to specific modules.
Fair enough. I would expect that pretty much everyone using follow_pfn
will at least want to switch to this one (as it's less bad and not
impossible to use correctly), but I'll squash this in:
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 90b527260edf..24b292fce8e5 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1659,8 +1659,8 @@ void free_pgd_range(struct mmu_gather *tlb,
unsigned long addr,
int
copy_page_range(struct vm_area_struct *dst_vma, struct vm_area_struct
*src_vma);
int follow_invalidate_pte(struct mm_struct *mm, unsigned long address,
- struct mmu_notifier_range *range, pte_t **ptepp, pmd_t **pmdpp,
- spinlock_t **ptlp);
+ struct mmu_notifier_range *range, pte_t **ptepp,
+ pmd_t **pmdpp, spinlock_t **ptlp);
int follow_pte(struct mm_struct *mm, unsigned long address,
pte_t **ptepp, spinlock_t **ptlp);
int follow_pfn(struct vm_area_struct *vma, unsigned long address,
diff --git a/mm/memory.c b/mm/memory.c
index 3632f7416248..c8679b15c004 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -4792,6 +4792,9 @@ int follow_invalidate_pte(struct mm_struct *mm,
unsigned long address,
* Only IO mappings and raw PFN mappings are allowed. The mmap semaphore
* should be taken for read.
*
+ * KVM uses this function. While it is arguably less bad than
+ * ``follow_pfn``, it is not a good general-purpose API.
+ *
* Return: zero on success, -ve otherwise.
*/
int follow_pte(struct mm_struct *mm, unsigned long address,
@@ -4809,6 +4812,9 @@ EXPORT_SYMBOL_GPL(follow_pte);
*
* Only IO mappings and raw PFN mappings are allowed.
*
+ * This function does not allow the caller to read the permissions
+ * of the PTE. Do not use it.
+ *
* Return: zero and the pfn at @pfn on success, -ve otherwise.
*/
int follow_pfn(struct vm_area_struct *vma, unsigned long address,
(apologies in advance if Thunderbird destroys the patch).
Paolo
next prev parent reply other threads:[~2021-02-08 20:00 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-05 10:32 [PATCH 0/2] KVM: do not assume PTE is writable after follow_pfn Paolo Bonzini
2021-02-05 10:32 ` [PATCH 1/2] mm: provide a sane PTE walking API for modules Paolo Bonzini
2021-02-05 13:49 ` Jason Gunthorpe
2021-02-08 17:39 ` Christoph Hellwig
2021-02-08 18:18 ` Paolo Bonzini [this message]
2021-02-09 8:14 ` Christoph Hellwig
2021-02-09 9:19 ` Paolo Bonzini
2021-02-05 10:32 ` [PATCH 2/2] KVM: do not assume PTE is writable after follow_pfn Paolo Bonzini
2021-02-05 15:43 ` kernel test robot
2021-02-05 17:41 ` kernel test robot
2021-02-05 18:14 ` [PATCH 0/2] " Peter Xu
2021-02-08 18:51 ` Jason Gunthorpe
2021-02-08 22:02 ` Peter Xu
2021-02-08 23:26 ` Jason Gunthorpe
2021-02-09 0:23 ` Peter Xu
2021-02-09 8:19 ` Christoph Hellwig
2021-02-09 10:02 ` Joao Martins
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=3b10057c-e117-89fa-1bd4-23fb5a4efb5f@redhat.com \
--to=pbonzini@redhat.com \
--cc=akpm@linux-foundation.org \
--cc=dan.j.williams@intel.com \
--cc=hch@infradead.org \
--cc=jgg@ziepe.ca \
--cc=kvm@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).