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An error on the description side occurs when the approach tries to access data or contacts that are in their address range but have not currently returned to system RAM. Hardware traps from the computer or laptop to the kernel and program counter (PC) are stored entirely on the stack.
Kernel threads never have a page fault: The web page error we’re talking about occurs when a virtual page is implemented as resident or returned from swap. Kmalloc () not only uses websites with kernels, but stays for life for Hawaiians). This is of course not the case for user-space pages, which A) is possibly lazy denoted (i.e. Reserved only as table page objects in malloc (), but truth is criticized. ‘With memset () or second dereferencing) and B) can be interchangeable in low memory conditions.
Why is it difficult for the kernel to access the user area via threads? Doesn’t copier_to_user () or copy_from_user () do this?
How do you fix page faults?
Check the position of the most linked page in the PMT.If a page error occurs, call the operating system to resolve the problem.Use the frame replacement algorithm to find the position of the main frame.Read data from the hard disk into memory.Upgrade your garden furniture from the side plan to work.
Great question with a word related to hardware. It is true that kernel threads are discouraged from accessing user space precisely because, in terms of a potential page error,Nits, many of them can occur when accessing users from non-paged / paged memory in space (remember that not all will work in kernel space, guaranteed in the above form). Copy_to / from will be a regular memcpy, but with a complete error page handler. In any case, this means that a potential page fault will be affected transparently (i.e. memory can be paged out) and everything will be fine. But there have certainly been complaints where the wrong approach involving memcpy to / from user memory would just work – worse, it would run very often because the page is very confusing for the residence and RAM number – and hence , unhandled errors can cause occasional panic. Hence the special decree to always use copy_from / to_user.
It was mentioned recently that kernel / user isolation repositories have become important for security reasons. This is due to numerous exploitation techniques (dereferencing NULL clauses is a very common and therefore powerful technique) in which fake ones And kernels (or code) can be created by web users in space (and therefore conveniently managed) memory, and this is when executed on a computer in the kernel.
Thus, most architectures get a page table bit that effectively prevents access to the page owned by the member in mode as well as in the kernel. Take arm64 for example, the item function is called PAN / PXN (Privileged Access / Execute Never).
Thus, copy_from / to now not only handles information errors, but also disables the PAN / PXN before the operation and restores it after.
- An exception is page error for vmalloc space: vmalloc () allocates memory and can be replaced, unlike kmalloc. The difference is in the installation (kmalloc uses GFP_KERNEL). This also indicates that kmalloc is more likely to fail (if there is no RAM for it), but certainly not due to a page error (it will return NULL, which would be a specific problem in itself).
As mentioned, Linux page error exception The manager can recognize exceptions caused by selection errors Persons intriggered by the transition, help the legally visited page a kind of process address space that hasn’t been allocated to be honest.
What causes a page fault?
A page fault occurs when a program tries to facilitate access to a block of memory that is not actually stored in physical RAM or RAM. However, a wrong page error can cause the approach to freeze or hang. This type of page fault can be repeated when a program tries to access a memory address that does not exist.
Storage scope descriptors allow an exception handler do the real work pretty efficiently. The
do_page_fault () function, i.e. page Emergency shutdown procedure for 80×86 architecture, compare a linear address because a page fault was caused for specific areas of memory current
process ; then understand it can figure out the correct way to handle the exception according to the general schema this is illustrated in the Ошибка страницы ядра
커널 페이지 오류
Error De Página Del Kernel
Erreur De Page Du Noyau
Falha De Página Do Kernel
Errore Di Pagina Del Kernel
Fel På Kärnan
Błąd Strony Jądra