Recent patch [1] disabled a self-snoop feature on a list of processor models with a known errata, so we are confident that the feature should work on remaining models also for other purposes than to speed up MTRR programming.
I would like to resurrect an old patch [2] that avoids calling clflush and wbinvd to invalidate caches when CPU supports selfsnoop. The patch was ported to latest Fedora kernel (5.1.16) and tested with CONFIG_CPA_DEBUG on INTEL_FAM6_IVYBRIDGE_X. The relevant ports of dmesg show: ... < hundreds of CPA protect messages, resulting from set_memory_rw CPA undo test in mm/init_64.c > CPA protect Rodata RO: 0xffffffffbd1fe000 - 0xffffffffbd1fefff PFN 1461fe req 8000000000000063 prevent 0000000000000002 CPA protect Rodata RO: 0xffff889c461fe000 - 0xffff889c461fefff PFN 1461fe req 8000000000000063 prevent 0000000000000002 Testing CPA: again Freeing unused kernel image memory: 2016K Freeing unused kernel image memory: 4K x86/mm: Checked W+X mappings: passed, no W+X pages found. rodata_test: all tests were successful x86/mm: Checking user space page tables x86/mm: Checked W+X mappings: passed, no W+X pages found. and from CPA selftest: CPA self-test: 4k 36352 large 4021 gb 0 x 81[ffff889b00098000-ffff889bdf7ff000] miss 133120 4k 180224 large 3740 gb 0 x 81[ffff889b00098000-ffff889bdf7ff000] miss 133120 4k 180224 large 3740 gb 0 x 81[ffff889b00098000-ffff889bdf7ff000] miss 133120 ok. [1] https://lkml.org/lkml/2019/6/27/828 [2] https://lkml.org/lkml/2009/4/8/508 Uros.
From 17cbad5d45b6ae26dbcfe02deba597c83cd63a0d Mon Sep 17 00:00:00 2001 From: Uros Bizjak <ubiz...@gmail.com> Date: Wed, 10 Jul 2019 15:01:44 +0200 Subject: [PATCH] Disable CPA cache flush for selfsnoop targets Signed-off-by: Uros Bizjak <ubiz...@gmail.com> --- arch/x86/mm/pageattr.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) diff --git a/arch/x86/mm/pageattr.c b/arch/x86/mm/pageattr.c index 6a9a77a403c9..8893ef5f70cd 100644 --- a/arch/x86/mm/pageattr.c +++ b/arch/x86/mm/pageattr.c @@ -1725,10 +1725,11 @@ static int change_page_attr_set_clr(unsigned long *addr, int numpages, goto out; /* - * No need to flush, when we did not set any of the caching - * attributes: + * No need to flush when CPU supports self snoop or + * when we did not set any of the caching attributes: */ - cache = !!pgprot2cachemode(mask_set); + cache = !static_cpu_has(X86_FEATURE_SELFSNOOP) && + pgprot2cachemode(mask_set); /* * On error; flush everything to be sure. -- 2.21.0
