linux/arch/x86
Thomas Gleixner 07f07f55a2 x86/speculation/mds: Conditionally clear CPU buffers on idle entry
Add a static key which controls the invocation of the CPU buffer clear
mechanism on idle entry. This is independent of other MDS mitigations
because the idle entry invocation to mitigate the potential leakage due to
store buffer repartitioning is only necessary on SMT systems.

Add the actual invocations to the different halt/mwait variants which
covers all usage sites. mwaitx is not patched as it's not available on
Intel CPUs.

The buffer clear is only invoked before entering the C-State to prevent
that stale data from the idling CPU is spilled to the Hyper-Thread sibling
after the Store buffer got repartitioned and all entries are available to
the non idle sibling.

When coming out of idle the store buffer is partitioned again so each
sibling has half of it available. Now CPU which returned from idle could be
speculatively exposed to contents of the sibling, but the buffers are
flushed either on exit to user space or on VMENTER.

When later on conditional buffer clearing is implemented on top of this,
then there is no action required either because before returning to user
space the context switch will set the condition flag which causes a flush
on the return to user path.

Note, that the buffer clearing on idle is only sensible on CPUs which are
solely affected by MSBDS and not any other variant of MDS because the other
MDS variants cannot be mitigated when SMT is enabled, so the buffer
clearing on idle would be a window dressing exercise.

This intentionally does not handle the case in the acpi/processor_idle
driver which uses the legacy IO port interface for C-State transitions for
two reasons:

 - The acpi/processor_idle driver was replaced by the intel_idle driver
   almost a decade ago. Anything Nehalem upwards supports it and defaults
   to that new driver.

 - The legacy IO port interface is likely to be used on older and therefore
   unaffected CPUs or on systems which do not receive microcode updates
   anymore, so there is no point in adding that.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Reviewed-by: Jon Masters <jcm@redhat.com>
Tested-by: Jon Masters <jcm@redhat.com>
2019-03-06 21:52:13 +01:00
..
boot x86/boot/compressed/64: Do not corrupt EDX on EFER.LME=1 setting 2019-02-06 18:56:18 +01:00
configs PCI: consolidate PCI config entry in drivers/pci 2018-11-23 11:45:34 +09:00
crypto Merge branch 'linus' of git://git.kernel.org/pub/scm/linux/kernel/git/herbert/crypto-2.6 2018-12-27 13:53:32 -08:00
entry x86/speculation/mds: Clear CPU buffers on exit to user 2019-03-06 21:52:13 +01:00
events perf/x86: Add check_period PMU callback 2019-02-11 11:46:43 +01:00
hyperv x86/hyper-v: Add HvFlushGuestAddressList hypercall support 2018-12-21 11:28:39 +01:00
ia32 x86/a.out: Clear the dump structure initially 2019-02-13 12:10:51 +01:00
include x86/speculation/mds: Conditionally clear CPU buffers on idle entry 2019-03-06 21:52:13 +01:00
kernel x86/speculation/mds: Conditionally clear CPU buffers on idle entry 2019-03-06 21:52:13 +01:00
kvm x86/kvm/vmx: Add MDS protection when L1D Flush is not active 2019-03-06 21:52:13 +01:00
lib x86: explicitly align IO accesses in memcpy_{to,from}io 2019-02-01 09:07:48 -08:00
math-emu Remove 'type' argument from access_ok() function 2019-01-03 18:57:57 -08:00
mm Revert "x86/fault: BUG() when uaccess helpers fault on kernel addresses" 2019-02-25 09:10:51 -08:00
net bpf: Add bpf_line_info support 2018-12-09 13:54:38 -08:00
oprofile
pci pci-v4.21-changes 2019-01-05 17:57:34 -08:00
platform x86/platform/UV: Use efi_runtime_lock to serialise BIOS calls 2019-02-15 15:19:56 +01:00
power
purgatory
ras
realmode
tools
um Remove 'type' argument from access_ok() function 2019-01-03 18:57:57 -08:00
video
xen xen: fixes for 5.0-rc3 2019-01-19 05:53:41 +12:00
.gitignore
Kbuild KVM: x86: Allow Qemu/KVM to use PVH entry point 2018-12-13 13:41:49 -05:00
Kconfig x86/resctrl: Avoid confusion over the new X86_RESCTRL config 2019-02-02 10:34:52 +01:00
Kconfig.cpu
Kconfig.debug
Makefile jump_label: move 'asm goto' support test to Kconfig 2019-01-06 09:46:51 +09:00
Makefile_32.cpu
Makefile.um x86, powerpc: Remove -funit-at-a-time compiler option entirely 2018-12-09 11:55:32 +01:00