From ea0765e835e084707abb7e14d84b572f5ffe4242 Mon Sep 17 00:00:00 2001 From: Changbin Du Date: Wed, 8 May 2019 23:21:29 +0800 Subject: [PATCH] Documentation: x86: convert pti.txt to reST This converts the plain text documentation to reStructuredText format and add it to Sphinx TOC tree. No essential content change. Signed-off-by: Changbin Du Reviewed-by: Mauro Carvalho Chehab Signed-off-by: Jonathan Corbet --- Documentation/x86/index.rst | 1 + Documentation/x86/{pti.txt => pti.rst} | 17 +++++++++++++---- 2 files changed, 14 insertions(+), 4 deletions(-) rename Documentation/x86/{pti.txt => pti.rst} (96%) diff --git a/Documentation/x86/index.rst b/Documentation/x86/index.rst index 85f1f44cc8ac..6719defc16f8 100644 --- a/Documentation/x86/index.rst +++ b/Documentation/x86/index.rst @@ -21,3 +21,4 @@ x86-specific Documentation protection-keys intel_mpx amd-memory-encryption + pti diff --git a/Documentation/x86/pti.txt b/Documentation/x86/pti.rst similarity index 96% rename from Documentation/x86/pti.txt rename to Documentation/x86/pti.rst index 5cd58439ad2d..4b858a9bad8d 100644 --- a/Documentation/x86/pti.txt +++ b/Documentation/x86/pti.rst @@ -1,9 +1,15 @@ +.. SPDX-License-Identifier: GPL-2.0 + +========================== +Page Table Isolation (PTI) +========================== + Overview ======== -Page Table Isolation (pti, previously known as KAISER[1]) is a +Page Table Isolation (pti, previously known as KAISER [1]_) is a countermeasure against attacks on the shared user/kernel address -space such as the "Meltdown" approach[2]. +space such as the "Meltdown" approach [2]_. To mitigate this class of attacks, we create an independent set of page tables for use only when running userspace applications. When @@ -60,6 +66,7 @@ Protection against side-channel attacks is important. But, this protection comes at a cost: 1. Increased Memory Use + a. Each process now needs an order-1 PGD instead of order-0. (Consumes an additional 4k per process). b. The 'cpu_entry_area' structure must be 2MB in size and 2MB @@ -68,6 +75,7 @@ this protection comes at a cost: is decompressed, but no space in the kernel image itself. 2. Runtime Cost + a. CR3 manipulation to switch between the page table copies must be done at interrupt, syscall, and exception entry and exit (it can be skipped when the kernel is interrupted, @@ -142,6 +150,7 @@ ideally doing all of these in parallel: interrupted, including nested NMIs. Using "-c" boosts the rate of NMIs, and using two -c with separate counters encourages nested NMIs and less deterministic behavior. + :: while true; do perf record -c 10000 -e instructions,cycles -a sleep 10; done @@ -182,5 +191,5 @@ that are worth noting here. tended to be TLB invalidation issues. Usually invalidating the wrong PCID, or otherwise missing an invalidation. -1. https://gruss.cc/files/kaiser.pdf -2. https://meltdownattack.com/meltdown.pdf +.. [1] https://gruss.cc/files/kaiser.pdf +.. [2] https://meltdownattack.com/meltdown.pdf