Re: [RFC PATCH 11/13] mm/vas: Introduce VAS segments - shareable address space regions

[Till Smejkal]

Hi Matthew,

On Mon, 13 Mar 2017, Matthew Wilcox wrote:
> On Mon, Mar 13, 2017 at 03:14:13PM -0700, Till Smejkal wrote:
> > +/**
> > + * Create a new VAS segment.
> > + *
> > + * @param[in] name:The name of the new VAS segment.
> > + * @param[in] start:   The address where the VAS segment 
> > begins.
> > + * @param[in] end: The address where the VAS segment ends.
> > + * @param[in] mode:The access rights for the VAS segment.
> > + *
> > + * @returns:   The VAS segment ID on success, -ERRNO 
> > otherwise.
> > + **/
> 
> Please follow the kernel-doc conventions, as described in
> Documentation/doc-guide/kernel-doc.rst.  Also, function documentation
> goes with the implementation, not the declaration.

Thank you for this pointer. I wasn't aware of this convention. I will change the
patches accordingly.

> > +/**
> > + * Get ID of the VAS segment belonging to a given name.
> > + *
> > + * @param[in] name:The name of the VAS segment for which 
> > the ID
> > + * should be returned.
> > + *
> > + * @returns:   The VAS segment ID on success, -ERRNO
> > + * otherwise.
> > + **/
> > +extern int vas_seg_find(const char *name);
> 
> So ... segments have names, and IDs ... and access permissions ...
> Why isn't this a special purpose filesystem?

We also thought about this. However, we decided against implementing them as a
special purpose filesystem, mainly because we could not think of a good way to
represent a VAS/VAS segment in this file system (should they be represented 
rather as
file or directory) and we weren't sure what a hierarchy in the filesystem would 
mean
for the underlying address spaces. Hence we decided against it and rather used a
combination of IDR and sysfs. However, I don't have any strong feelings and 
would
also reimplement them as a special purpose filesystem if people rather like 
them to
be one.

Till

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Re: [RFC PATCH 11/13] mm/vas: Introduce VAS segments - shareable address space regions

[Matthew Wilcox]

On Mon, Mar 13, 2017 at 03:14:13PM -0700, Till Smejkal wrote:
> +/**
> + * Create a new VAS segment.
> + *
> + * @param[in] name:  The name of the new VAS segment.
> + * @param[in] start: The address where the VAS segment begins.
> + * @param[in] end:   The address where the VAS segment ends.
> + * @param[in] mode:  The access rights for the VAS segment.
> + *
> + * @returns: The VAS segment ID on success, -ERRNO otherwise.
> + **/

Please follow the kernel-doc conventions, as described in
Documentation/doc-guide/kernel-doc.rst.  Also, function documentation
goes with the implementation, not the declaration.

> +/**
> + * Get ID of the VAS segment belonging to a given name.
> + *
> + * @param[in] name:  The name of the VAS segment for which the ID
> + *   should be returned.
> + *
> + * @returns: The VAS segment ID on success, -ERRNO
> + *   otherwise.
> + **/
> +extern int vas_seg_find(const char *name);

So ... segments have names, and IDs ... and access permissions ...
Why isn't this a special purpose filesystem?


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[RFC PATCH 11/13] mm/vas: Introduce VAS segments - shareable address space regions

[Till Smejkal]

VAS segments are an extension to first class virtual address spaces that
can be used to share specific memory regions between multiple first class
virtual address spaces. VAS segments have a specific size and position in a
virtual address space and can thereby be used to share in-memory pointer
based data structures between multiple address spaces as well as other
in-memory data without the need to represent them in mmap-able files or
use shmem.

Similar to first class virtual address spaces, VAS segments must be created
and destroyed explicitly by a user. The system will never automatically
destroy or create a virtual segment. Via attaching a VAS segment to a first
class virtual address space, the memory that is contained in the VAS
segment can be accessed and changed.

Signed-off-by: Till Smejkal 
Signed-off-by: Marco Benatto 
---
 arch/x86/entry/syscalls/syscall_32.tbl |7 +
 arch/x86/entry/syscalls/syscall_64.tbl |7 +
 include/linux/syscalls.h   |   10 +
 include/linux/vas.h|  114 +++
 include/linux/vas_types.h  |   91 ++-
 include/uapi/asm-generic/unistd.h  |   16 +-
 include/uapi/linux/vas.h   |   12 +
 kernel/sys_ni.c|7 +
 mm/vas.c   | 1234 ++--
 9 files changed, 1451 insertions(+), 47 deletions(-)

diff --git a/arch/x86/entry/syscalls/syscall_32.tbl 
b/arch/x86/entry/syscalls/syscall_32.tbl
index 8c553eef8c44..a4f91d14a856 100644
--- a/arch/x86/entry/syscalls/syscall_32.tbl
+++ b/arch/x86/entry/syscalls/syscall_32.tbl
@@ -398,3 +398,10 @@
 389i386active_vas  sys_active_vas
 390i386vas_getattr sys_vas_getattr
 391i386vas_setattr sys_vas_setattr
+392i386vas_seg_create  sys_vas_seg_create
+393i386vas_seg_delete  sys_vas_seg_delete
+394i386vas_seg_findsys_vas_seg_find
+395i386vas_seg_attach  sys_vas_seg_attach
+396i386vas_seg_detach  sys_vas_seg_detach
+397i386vas_seg_getattr sys_vas_seg_getattr
+398i386vas_seg_setattr sys_vas_seg_setattr
diff --git a/arch/x86/entry/syscalls/syscall_64.tbl 
b/arch/x86/entry/syscalls/syscall_64.tbl
index 72f1f0495710..a0f9503c3d28 100644
--- a/arch/x86/entry/syscalls/syscall_64.tbl
+++ b/arch/x86/entry/syscalls/syscall_64.tbl
@@ -347,6 +347,13 @@
 338common  active_vas  sys_active_vas
 339common  vas_getattr sys_vas_getattr
 340common  vas_setattr sys_vas_setattr
+341common  vas_seg_create  sys_vas_seg_create
+342common  vas_seg_delete  sys_vas_seg_delete
+343common  vas_seg_findsys_vas_seg_find
+344common  vas_seg_attach  sys_vas_seg_attach
+345common  vas_seg_detach  sys_vas_seg_detach
+346common  vas_seg_getattr sys_vas_seg_getattr
+347common  vas_seg_setattr sys_vas_seg_setattr
 
 #
 # x32-specific system call numbers start at 512 to avoid cache impact
diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index fdea27d37c96..7380dcdc4bc1 100644
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h
@@ -66,6 +66,7 @@ struct perf_event_attr;
 struct file_handle;
 struct sigaltstack;
 struct vas_attr;
+struct vas_seg_attr;
 union bpf_attr;
 
 #include 
@@ -914,4 +915,13 @@ asmlinkage long sys_active_vas(void);
 asmlinkage long sys_vas_getattr(int vid, struct vas_attr __user *attr);
 asmlinkage long sys_vas_setattr(int vid, struct vas_attr __user *attr);
 
+asmlinkage long sys_vas_seg_create(const char __user *name, unsigned long 
start,
+  unsigned long end, umode_t mode);
+asmlinkage long sys_vas_seg_delete(int sid);
+asmlinkage long sys_vas_seg_find(const char __user *name);
+asmlinkage long sys_vas_seg_attach(int vid, int sid, int type);
+asmlinkage long sys_vas_seg_detach(int vid, int sid);
+asmlinkage long sys_vas_seg_getattr(int sid, struct vas_seg_attr __user *attr);
+asmlinkage long sys_vas_seg_setattr(int sid, struct vas_seg_attr __user *attr);
+
 #endif
diff --git a/include/linux/vas.h b/include/linux/vas.h
index 6a72e42f96d2..376b9fa1ee27 100644
--- a/include/linux/vas.h
+++ b/include/linux/vas.h
@@ -138,6 +138,120 @@ extern int vas_setattr(int vid, struct vas_attr *attr);
 
 
 /***
+ * Management of VAS segments
+ ***/
+
+/**
+ * Lock and unlock helper for VAS segments.
+ **/
+#define vas_seg_lock(seg) mutex_lock(&(seg)->mtx)
+#define vas_seg_unlock(seg) mutex_unlock(&(seg)->mtx)
+
+/**
+ * Create a new VAS segment.
+ *
+ * @param[in] name:The name of the new VAS segment.
+ * @param[in] start:   The address where the VAS segment begins.
+ * @param[in] end: The address where the VAS segment ends.
+ * @param[in] mode:The access rights for the VAS segment.
+ *