Re: [PATCH V5 1/2] perf ignore LBR and extra_regs
From: Paolo Bonzini
Date: Mon Jul 14 2014 - 07:55:33 EST
Il 10/07/2014 12:59, kan.liang@xxxxxxxxx ha scritto:
From: Kan Liang <kan.liang@xxxxxxxxx>
x86, perf: Protect LBR and extra_regs against KVM lying
With -cpu host, KVM reports LBR and extra_regs support, if the host has support.
When the guest perf driver tries to access LBR or extra_regs MSR,
it #GPs all MSR accesses,since KVM doesn't handle LBR and extra_regs support.
So check the related MSRs access right once at initialization time to avoid the error access at runtime.
For reproducing the issue, please build the kernel with CONFIG_KVM_INTEL = y (for host kernel).
And CONFIG_PARAVIRT = n and CONFIG_KVM_GUEST = n (for guest kernel).
I'm not sure this is a useful patch.
This is #GP'ing just because of a limitation in the PMU; just compile
the kernel with CONFIG_PARAVIRT, or split the "rdmsr is always
rdmsr_safe" behavior out of CONFIG_PARAVIRT and into a new Kconfig symbol.
In fact there's no reason why LBR cannot be virtualized (though it does
need support from the processor), and it may even be possible to support
OFFCORE_RSP_X in the KVM virtual PMU.
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/