linux-kernel - [tip:x86/urgent] x86/CPU/AMD: Don't force the CPB cap when running under a hypervisor

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Date:   Fri, 24 May 2019 01:06:11 -0700
From:   tip-bot for Frank van der Linden <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     luto@...nel.org, mingo@...nel.org, fllinden@...zon.com,
        hpa@...or.com, linux-kernel@...r.kernel.org, tglx@...utronix.de,
        torvalds@...ux-foundation.org, bp@...e.de, peterz@...radead.org
Subject: [tip:x86/urgent] x86/CPU/AMD: Don't force the CPB cap when running
 under a hypervisor

Commit-ID:  2ac44ab608705948564791ce1d15d43ba81a1e38
Gitweb:     https://git.kernel.org/tip/2ac44ab608705948564791ce1d15d43ba81a1e38
Author:     Frank van der Linden <fllinden@...zon.com>
AuthorDate: Wed, 22 May 2019 22:17:45 +0000
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Fri, 24 May 2019 08:50:32 +0200

x86/CPU/AMD: Don't force the CPB cap when running under a hypervisor

For F17h AMD CPUs, the CPB capability ('Core Performance Boost') is forcibly set,
because some versions of that chip incorrectly report that they do not have it.

However, a hypervisor may filter out the CPB capability, for good
reasons. For example, KVM currently does not emulate setting the CPB
bit in MSR_K7_HWCR, and unchecked MSR access errors will be thrown
when trying to set it as a guest:

	unchecked MSR access error: WRMSR to 0xc0010015 (tried to write 0x0000000001000011) at rIP: 0xffffffff890638f4 (native_write_msr+0x4/0x20)

	Call Trace:
	boost_set_msr+0x50/0x80 [acpi_cpufreq]
	cpuhp_invoke_callback+0x86/0x560
	sort_range+0x20/0x20
	cpuhp_thread_fun+0xb0/0x110
	smpboot_thread_fn+0xef/0x160
	kthread+0x113/0x130
	kthread_create_worker_on_cpu+0x70/0x70
	ret_from_fork+0x35/0x40

To avoid this issue, don't forcibly set the CPB capability for a CPU
when running under a hypervisor.

Signed-off-by: Frank van der Linden <fllinden@...zon.com>
Acked-by: Borislav Petkov <bp@...e.de>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: bp@...en8.de
Cc: jiaxun.yang@...goat.com
Fixes: 0237199186e7 ("x86/CPU/AMD: Set the CPB bit unconditionally on F17h")
Link: http://lkml.kernel.org/r/20190522221745.GA15789@dev-dsk-fllinden-2c-c1893d73.us-west-2.amazon.com
[ Minor edits to the changelog. ]
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 arch/x86/kernel/cpu/amd.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
index 80a405c2048a..8d4e50428b68 100644
--- a/arch/x86/kernel/cpu/amd.c
+++ b/arch/x86/kernel/cpu/amd.c
@@ -824,8 +824,11 @@ static void init_amd_zn(struct cpuinfo_x86 *c)
 {
 	set_cpu_cap(c, X86_FEATURE_ZEN);
 
-	/* Fix erratum 1076: CPB feature bit not being set in CPUID. */
-	if (!cpu_has(c, X86_FEATURE_CPB))
+	/*
+	 * Fix erratum 1076: CPB feature bit not being set in CPUID.
+	 * Always set it, except when running under a hypervisor.
+	 */
+	if (!cpu_has(c, X86_FEATURE_HYPERVISOR) && !cpu_has(c, X86_FEATURE_CPB))
 		set_cpu_cap(c, X86_FEATURE_CPB);
 }