diff options
Diffstat (limited to 'Documentation')
| -rw-r--r-- | Documentation/filesystems/porting | 5 | ||||
| -rw-r--r-- | Documentation/virtual/kvm/api.txt | 5 | ||||
| -rw-r--r-- | Documentation/x86/mds.rst | 44 |
3 files changed, 14 insertions, 40 deletions
diff --git a/Documentation/filesystems/porting b/Documentation/filesystems/porting index cf43bc4dbf31..a60fa516d4cb 100644 --- a/Documentation/filesystems/porting +++ b/Documentation/filesystems/porting @@ -638,3 +638,8 @@ in your dentry operations instead. inode to d_splice_alias() will also do the right thing (equivalent of d_add(dentry, NULL); return NULL;), so that kind of special cases also doesn't need a separate treatment. +-- +[mandatory] + DCACHE_RCUACCESS is gone; having an RCU delay on dentry freeing is the + default. DCACHE_NORCU opts out, and only d_alloc_pseudo() has any + business doing so. diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt index ba8927c0d45c..a1b8e6d92298 100644 --- a/Documentation/virtual/kvm/api.txt +++ b/Documentation/virtual/kvm/api.txt @@ -3790,8 +3790,9 @@ The ioctl clears the dirty status of pages in a memory slot, according to the bitmap that is passed in struct kvm_clear_dirty_log's dirty_bitmap field. Bit 0 of the bitmap corresponds to page "first_page" in the memory slot, and num_pages is the size in bits of the input bitmap. -Both first_page and num_pages must be a multiple of 64. For each bit -that is set in the input bitmap, the corresponding page is marked "clean" +first_page must be a multiple of 64; num_pages must also be a multiple of +64 unless first_page + num_pages is the size of the memory slot. For each +bit that is set in the input bitmap, the corresponding page is marked "clean" in KVM's dirty bitmap, and dirty tracking is re-enabled for that page (for example via write-protection, or by clearing the dirty bit in a page table entry). diff --git a/Documentation/x86/mds.rst b/Documentation/x86/mds.rst index 534e9baa4e1d..5d4330be200f 100644 --- a/Documentation/x86/mds.rst +++ b/Documentation/x86/mds.rst @@ -142,45 +142,13 @@ Mitigation points mds_user_clear. The mitigation is invoked in prepare_exit_to_usermode() which covers - most of the kernel to user space transitions. There are a few exceptions - which are not invoking prepare_exit_to_usermode() on return to user - space. These exceptions use the paranoid exit code. + all but one of the kernel to user space transitions. The exception + is when we return from a Non Maskable Interrupt (NMI), which is + handled directly in do_nmi(). - - Non Maskable Interrupt (NMI): - - Access to sensible data like keys, credentials in the NMI context is - mostly theoretical: The CPU can do prefetching or execute a - misspeculated code path and thereby fetching data which might end up - leaking through a buffer. - - But for mounting other attacks the kernel stack address of the task is - already valuable information. So in full mitigation mode, the NMI is - mitigated on the return from do_nmi() to provide almost complete - coverage. - - - Double fault (#DF): - - A double fault is usually fatal, but the ESPFIX workaround, which can - be triggered from user space through modify_ldt(2) is a recoverable - double fault. #DF uses the paranoid exit path, so explicit mitigation - in the double fault handler is required. - - - Machine Check Exception (#MC): - - Another corner case is a #MC which hits between the CPU buffer clear - invocation and the actual return to user. As this still is in kernel - space it takes the paranoid exit path which does not clear the CPU - buffers. So the #MC handler repopulates the buffers to some - extent. Machine checks are not reliably controllable and the window is - extremly small so mitigation would just tick a checkbox that this - theoretical corner case is covered. To keep the amount of special - cases small, ignore #MC. - - - Debug Exception (#DB): - - This takes the paranoid exit path only when the INT1 breakpoint is in - kernel space. #DB on a user space address takes the regular exit path, - so no extra mitigation required. + (The reason that NMI is special is that prepare_exit_to_usermode() can + enable IRQs. In NMI context, NMIs are blocked, and we don't want to + enable IRQs with NMIs blocked.) 2. C-State transition |