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author | Tim Chen <tim.c.chen@linux.intel.com> | 2018-11-25 19:33:46 +0100 |
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committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2018-12-05 19:32:03 +0100 |
commit | 69985a2cae82ebca281da7e7275bba7ef2b3dca8 (patch) | |
tree | a9b4580a66662bf7754fcc04c05929793653bbe7 /arch/x86/kernel/process.c | |
parent | 711875432218e9e819bfde90cb99c61569c8fa90 (diff) | |
download | linux-stable-69985a2cae82ebca281da7e7275bba7ef2b3dca8.tar.gz linux-stable-69985a2cae82ebca281da7e7275bba7ef2b3dca8.tar.bz2 linux-stable-69985a2cae82ebca281da7e7275bba7ef2b3dca8.zip |
x86/speculation: Prepare for per task indirect branch speculation control
commit 5bfbe3ad5840d941b89bcac54b821ba14f50a0ba upstream
To avoid the overhead of STIBP always on, it's necessary to allow per task
control of STIBP.
Add a new task flag TIF_SPEC_IB and evaluate it during context switch if
SMT is active and flag evaluation is enabled by the speculation control
code. Add the conditional evaluation to x86_virt_spec_ctrl() as well so the
guest/host switch works properly.
This has no effect because TIF_SPEC_IB cannot be set yet and the static key
which controls evaluation is off. Preparatory patch for adding the control
code.
[ tglx: Simplify the context switch logic and make the TIF evaluation
depend on SMP=y and on the static key controlling the conditional
update. Rename it to TIF_SPEC_IB because it controls both STIBP and
IBPB ]
Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Ingo Molnar <mingo@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Jiri Kosina <jkosina@suse.cz>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Cc: David Woodhouse <dwmw@amazon.co.uk>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Dave Hansen <dave.hansen@intel.com>
Cc: Casey Schaufler <casey.schaufler@intel.com>
Cc: Asit Mallick <asit.k.mallick@intel.com>
Cc: Arjan van de Ven <arjan@linux.intel.com>
Cc: Jon Masters <jcm@redhat.com>
Cc: Waiman Long <longman9394@gmail.com>
Cc: Greg KH <gregkh@linuxfoundation.org>
Cc: Dave Stewart <david.c.stewart@intel.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: stable@vger.kernel.org
Link: https://lkml.kernel.org/r/20181125185005.176917199@linutronix.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'arch/x86/kernel/process.c')
-rw-r--r-- | arch/x86/kernel/process.c | 20 |
1 files changed, 18 insertions, 2 deletions
diff --git a/arch/x86/kernel/process.c b/arch/x86/kernel/process.c index 70e9832379e1..574b144d2b53 100644 --- a/arch/x86/kernel/process.c +++ b/arch/x86/kernel/process.c @@ -404,11 +404,17 @@ static __always_inline void amd_set_ssb_virt_state(unsigned long tifn) static __always_inline void __speculation_ctrl_update(unsigned long tifp, unsigned long tifn) { + unsigned long tif_diff = tifp ^ tifn; u64 msr = x86_spec_ctrl_base; bool updmsr = false; - /* If TIF_SSBD is different, select the proper mitigation method */ - if ((tifp ^ tifn) & _TIF_SSBD) { + /* + * If TIF_SSBD is different, select the proper mitigation + * method. Note that if SSBD mitigation is disabled or permanentely + * enabled this branch can't be taken because nothing can set + * TIF_SSBD. + */ + if (tif_diff & _TIF_SSBD) { if (static_cpu_has(X86_FEATURE_VIRT_SSBD)) { amd_set_ssb_virt_state(tifn); } else if (static_cpu_has(X86_FEATURE_LS_CFG_SSBD)) { @@ -420,6 +426,16 @@ static __always_inline void __speculation_ctrl_update(unsigned long tifp, } } + /* + * Only evaluate TIF_SPEC_IB if conditional STIBP is enabled, + * otherwise avoid the MSR write. + */ + if (IS_ENABLED(CONFIG_SMP) && + static_branch_unlikely(&switch_to_cond_stibp)) { + updmsr |= !!(tif_diff & _TIF_SPEC_IB); + msr |= stibp_tif_to_spec_ctrl(tifn); + } + if (updmsr) wrmsrl(MSR_IA32_SPEC_CTRL, msr); } |