Messages in this thread | | | From | Andy Lutomirski <> | Subject | [PATCH 0/3] x86/paravirt: Fix baremetal paravirt MSR ops | Date | Wed, 16 Sep 2015 16:33:11 -0700 |
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Setting CONFIG_PARAVIRT=y has an unintended side effect: it silently turns all rdmsr and wrmsr operations into the safe variants without any checks that the operations actually succeed.
This is IMO awful: it papers over bugs. In particular, KVM gueests might be unwittingly depending on this behavior because CONFIG_KVM_GUEST currently depends on CONFIG_PARAVIRT. I'm not aware of any such problems, but applying this series would be a good way to shake them out.
Fix it so that the MSR operations work the same on CONFIG_PARAVIRT=n and CONFIG_PARAVIRT=y as long as Xen isn't being used. The Xen maintainers are welcome to make a similar change on top of this.
Since there's plenty of time before the next merge window, I think we should apply and fix anything that breaks.
Doing this is probably a prerequisite to sanely decoupling CONFIG_KVM_GUEST and CONFIG_PARAVIRT, which would probably make Arjan and the rest of the Clear Containers people happy :)
Andy Lutomirski (3): x86/paravirt: Add _safe to the read_msr and write_msr PV hooks x86/paravirt: Add paravirt_{read,write}_msr x86/paravirt: Make "unsafe" MSR accesses unsafe even if PARAVIRT=y
arch/x86/include/asm/paravirt.h | 45 +++++++++++++++++++++-------------- arch/x86/include/asm/paravirt_types.h | 12 +++++++--- arch/x86/kernel/paravirt.c | 6 +++-- arch/x86/xen/enlighten.c | 27 +++++++++++++++++++-- 4 files changed, 65 insertions(+), 25 deletions(-)
-- 2.4.3
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