On Wed, Mar 10, 2021 at 08:16:24PM +0100, Alejandro Colomar (man-pages) wrote: > Hi Peter, > > Please see a few comments below. > > Thanks, > > Alex > > On 3/4/21 5:31 PM, Peter Xu wrote: > > Write-protect mode is supported starting from Linux 5.7. > > > > Signed-off-by: Peter Xu <peterx@xxxxxxxxxx> > > --- > > man2/userfaultfd.2 | 98 +++++++++++++++++++++++++++++++++++++++++++++- > > 1 file changed, 96 insertions(+), 2 deletions(-) > > > > diff --git a/man2/userfaultfd.2 b/man2/userfaultfd.2 > > index 0cd426a8a..426307bcf 100644 > > --- a/man2/userfaultfd.2 > > +++ b/man2/userfaultfd.2 > > @@ -78,6 +78,30 @@ all memory ranges that were registered with the object are unregistered > > and unread events are flushed. > > .\" > > .PP > > +Currently, userfaultfd supports two modes of registration: > > "Currently" > > Than word is quite unstable and unprecise. > I think it would be better to use an absolute reference, such as "Since > Linux x.y, ...". I decided to remove the "Currently" and put the "(since x.y)" into each mode: diff --git a/man2/userfaultfd.2 b/man2/userfaultfd.2 index 426307bcf..1132f52a3 100644 --- a/man2/userfaultfd.2 +++ b/man2/userfaultfd.2 @@ -78,9 +78,9 @@ all memory ranges that were registered with the object are unregistered and unread events are flushed. .\" .PP -Currently, userfaultfd supports two modes of registration: +Userfaultfd supports two modes of registration: .TP -.B UFFDIO_REGISTER_MODE_MISSING +.BR UFFDIO_REGISTER_MODE_MISSING " (since 4.10)" When registered with .B UFFDIO_REGISTER_MODE_MISSING mode, the userspace will receive a page fault message when a missing page is @@ -91,7 +91,7 @@ or an .B UFFDIO_ZEROPAGE ioctl. .TP -.B UFFDIO_REGISTER_MODE_WP +.BR UFFDIO_REGISTER_MODE_WP " (since 5.7)" When registered with .B UFFDIO_REGISTER_MODE_WP mode, the userspace will receive a page fault message when a write-protected > > > +.TP > > +.B UFFDIO_REGISTER_MODE_MISSING > > +When registered with > > +.B UFFDIO_REGISTER_MODE_MISSING > > +mode, the userspace will receive a page fault message when a missing page is > > +accessed. The faulted thread will be stopped from execution until the page > > +fault is resolved from the userspace by either an > > +.B UFFDIO_COPY > > +or an > > +.B UFFDIO_ZEROPAGE > > +ioctl. > > +.TP > > +.B UFFDIO_REGISTER_MODE_WP > > +When registered with > > +.B UFFDIO_REGISTER_MODE_WP > > +mode, the userspace will receive a page fault message when a write-protected > > +page is written. The faulted thread will be stopped from execution until the > > Please, use "semantic newlines". > > $ man 7 man-pages |sed -n '/semantic newlines/,/^$/p' > Use semantic newlines > In the source of a manual page, new sentences should be > started on new lines, and long sentences should split into > lines at clause breaks (commas, semicolons, colons, and so > on). This convention, sometimes known as "semantic new- > lines", makes it easier to see the effect of patches, which > often operate at the level of individual sentences or sen- > tence clauses. Will do. > > > > > +userspace un-write-protect the page using an > > +.B UFFDIO_WRITEPROTECT > > +ioctl. > > +.PP > > +Multiple modes can be enabled at the same time for the same memory range. > > +.PP > > Since Linux 4.14, userfaultfd page fault message can selectively embed faulting > > thread ID information into the fault message. One needs to enable this feature > > explicitly using the > > @@ -144,6 +168,16 @@ single threaded non-cooperative userfaultfd manager implementations. > > .\" and limitations remaining in 4.11 > > .\" Maybe it's worth adding a dedicated sub-section... > > .\" > > +.PP > > +Starting from Linux 5.7, userfaultfd is able to do synchronous page dirty > > +tracking using the new write-protection register mode. One should check > > +against the feature bit > > +.B UFFD_FEATURE_PAGEFAULT_FLAG_WP > > +before using this feature. Similar to the original userfaultfd missing mode, > > +the write-protect mode will generate an userfaultfd message when the protected > > +page is written. The user needs to resolve the page fault by unprotecting the > > +faulted page and kick the faulted thread to continue. For more information, > > +please read the "Userfaultfd write-protect mode" section below. > > .SS Userfaultfd operation > > After the userfaultfd object is created with > > .BR userfaultfd (), > > @@ -219,6 +253,62 @@ userfaultfd can be used only with anonymous private memory mappings. > > Since Linux 4.11, > > userfaultfd can be also used with hugetlbfs and shared memory mappings. > > .\" > > +.SS Userfaultfd write-protect mode > > +Since Linux 5.7, userfaultfd supports write-protect mode. The user needs to > > +first check availability of this feature using > > +.B UFFDIO_API > > +ioctl against the feature bit > > +.BR UFFD_FEATURE_PAGEFAULT_FLAG_WP . > > +.PP > > +To register with userfaultfd write-protect mode, the user needs to initiate the > > +.B UFFDIO_REGISTER > > +ioctl with mode > > +.B UFFDIO_REGISTER_MODE_WP > > +set. Note that it's legal to monitor the same memory range with multiple > > +modes. For example, the user can do > > +.B UFFDIO_REGISTER > > +with the mode set to > > +.BR UFFDIO_REGISTER_MODE_MISSING\ |\ UFFDIO_REGISTER_MODE_WP . > > Please use quotes when possible: > > .BR "asdasd asdsadf dfgsdfg dsf" . Fixed. > > > +When there is only > > +.B UFFDIO_REGISTER_MODE_WP > > +registered, the userspace will > > +.I not > > +receive any message when a missing page is written. Instead, the userspace > > +will only receive a write-protect page fault message when an existing but > > +write-protected page got written. > > +.PP > > +After the > > +.B UFFDIO_REGISTER > > +ioctl completed with > > +.B UFFDIO_REGISTER_MODE_WP > > +mode set, the user can write-protect any existing memory within the range using > > +the ioctl > > +.B UFFDIO_WRITEPROTECT > > +where > > +.I uffdio_writeprotect.mode > > +should be set to > > +.BR UFFDIO_WRITEPROTECT_MODE_WP . > > +.PP > > +When a write-protect event happens, the userspace will receive a page fault > > +message whose > > +.I uffd_msg.pagefault.flags > > +will be with > > +.B UFFD_PAGEFAULT_FLAG_WP > > +flag set. Note: since only writes can trigger such kind of fault, > > +write-protect messages will always be with > > +.B UFFD_PAGEFAULT_FLAG_WRITE > > +bit set too along with > > +.BR UFFD_PAGEFAULT_FLAG_WP . > > +.PP > > +To resolve a write-protection page fault, the user should initiate another > > +.B UFFDIO_WRITEPROTECT > > +ioctl whose > > +.I uffd_msg.pagefault.flags > > +should have the flag > > +.BR UFFDIO_WRITEPROTECT_MODE_WP > > .B Fixed. Thanks, -- Peter Xu
