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Re: [PATCH v4 02/12] mm/memfd: Introduce MFD_INACCESSIBLE flag
From: |
Chao Peng |
Subject: |
Re: [PATCH v4 02/12] mm/memfd: Introduce MFD_INACCESSIBLE flag |
Date: |
Mon, 24 Jan 2022 21:29:36 +0800 |
User-agent: |
Mutt/1.9.4 (2018-02-28) |
On Fri, Jan 21, 2022 at 03:50:55PM +0000, Steven Price wrote:
> On 18/01/2022 13:21, Chao Peng wrote:
> > Introduce a new memfd_create() flag indicating the content of the
> > created memfd is inaccessible from userspace. It does this by force
> > setting F_SEAL_INACCESSIBLE seal when the file is created. It also set
> > F_SEAL_SEAL to prevent future sealing, which means, it can not coexist
> > with MFD_ALLOW_SEALING.
> >
> > The pages backed by such memfd will be used as guest private memory in
> > confidential computing environments such as Intel TDX/AMD SEV. Since
> > page migration/swapping is not yet supported for such usages so these
> > pages are currently marked as UNMOVABLE and UNEVICTABLE which makes
> > them behave like long-term pinned pages.
> >
> > Signed-off-by: Chao Peng <chao.p.peng@linux.intel.com>
> > ---
> > include/uapi/linux/memfd.h | 1 +
> > mm/memfd.c | 20 +++++++++++++++++++-
> > 2 files changed, 20 insertions(+), 1 deletion(-)
> >
> > diff --git a/include/uapi/linux/memfd.h b/include/uapi/linux/memfd.h
> > index 7a8a26751c23..48750474b904 100644
> > --- a/include/uapi/linux/memfd.h
> > +++ b/include/uapi/linux/memfd.h
> > @@ -8,6 +8,7 @@
> > #define MFD_CLOEXEC 0x0001U
> > #define MFD_ALLOW_SEALING 0x0002U
> > #define MFD_HUGETLB 0x0004U
> > +#define MFD_INACCESSIBLE 0x0008U
> >
> > /*
> > * Huge page size encoding when MFD_HUGETLB is specified, and a huge page
> > diff --git a/mm/memfd.c b/mm/memfd.c
> > index 9f80f162791a..26998d96dc11 100644
> > --- a/mm/memfd.c
> > +++ b/mm/memfd.c
> > @@ -245,16 +245,19 @@ long memfd_fcntl(struct file *file, unsigned int cmd,
> > unsigned long arg)
> > #define MFD_NAME_PREFIX_LEN (sizeof(MFD_NAME_PREFIX) - 1)
> > #define MFD_NAME_MAX_LEN (NAME_MAX - MFD_NAME_PREFIX_LEN)
> >
> > -#define MFD_ALL_FLAGS (MFD_CLOEXEC | MFD_ALLOW_SEALING | MFD_HUGETLB)
> > +#define MFD_ALL_FLAGS (MFD_CLOEXEC | MFD_ALLOW_SEALING | MFD_HUGETLB | \
> > + MFD_INACCESSIBLE)
> >
> > SYSCALL_DEFINE2(memfd_create,
> > const char __user *, uname,
> > unsigned int, flags)
> > {
> > + struct address_space *mapping;
> > unsigned int *file_seals;
> > struct file *file;
> > int fd, error;
> > char *name;
> > + gfp_t gfp;
> > long len;
> >
> > if (!(flags & MFD_HUGETLB)) {
> > @@ -267,6 +270,10 @@ SYSCALL_DEFINE2(memfd_create,
> > return -EINVAL;
> > }
> >
> > + /* Disallow sealing when MFD_INACCESSIBLE is set. */
> > + if (flags & MFD_INACCESSIBLE && flags & MFD_ALLOW_SEALING)
> > + return -EINVAL;
> > +
> > /* length includes terminating zero */
> > len = strnlen_user(uname, MFD_NAME_MAX_LEN + 1);
> > if (len <= 0)
> > @@ -315,6 +322,17 @@ SYSCALL_DEFINE2(memfd_create,
> > *file_seals &= ~F_SEAL_SEAL;
> > }
> >
> > + if (flags & MFD_INACCESSIBLE) {
> > + mapping = file_inode(file)->i_mapping;
> > + gfp = mapping_gfp_mask(mapping);
> > + gfp &= ~__GFP_MOVABLE;
> > + mapping_set_gfp_mask(mapping, gfp);
> > + mapping_set_unevictable(mapping);
> > +
> > + file_seals = memfd_file_seals_ptr(file);
> > + *file_seals &= F_SEAL_SEAL | F_SEAL_INACCESSIBLE;
>
> This looks backwards - the flags should be set on *file_seals, but here
> you are unsetting all other flags.
Thanks Steve. '|=' actually should be used here.
Chao
>
> Steve
>
> > + }
> > +
> > fd_install(fd, file);
> > kfree(name);
> > return fd;
> >
- [PATCH v4 00/12] KVM: mm: fd-based approach for supporting KVM guest private memory, Chao Peng, 2022/01/18
- [PATCH v4 01/12] mm/shmem: Introduce F_SEAL_INACCESSIBLE, Chao Peng, 2022/01/18
- [PATCH v4 02/12] mm/memfd: Introduce MFD_INACCESSIBLE flag, Chao Peng, 2022/01/18
- [PATCH v4 03/12] mm: Introduce memfile_notifier, Chao Peng, 2022/01/18
- [PATCH v4 04/12] mm/shmem: Support memfile_notifier, Chao Peng, 2022/01/18
- [PATCH v4 05/12] KVM: Extend the memslot to support fd-based private memory, Chao Peng, 2022/01/18
- [PATCH v4 06/12] KVM: Use kvm_userspace_memory_region_ext, Chao Peng, 2022/01/18
- [PATCH v4 07/12] KVM: Add KVM_EXIT_MEMORY_ERROR exit, Chao Peng, 2022/01/18
- [PATCH v4 08/12] KVM: Use memfile_pfn_ops to obtain pfn for private pages, Chao Peng, 2022/01/18
- [PATCH v4 09/12] KVM: Handle page fault for private memory, Chao Peng, 2022/01/18
- [PATCH v4 10/12] KVM: Register private memslot to memory backing store, Chao Peng, 2022/01/18
- [PATCH v4 11/12] KVM: Zap existing KVM mappings when pages changed in the private fd, Chao Peng, 2022/01/18
- [PATCH v4 12/12] KVM: Expose KVM_MEM_PRIVATE, Chao Peng, 2022/01/18