linux-kernel - Re: [PATCH] KVM: SVM: fix trashing of MSR_TSC

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Date:	Thu, 7 Jul 2016 12:41:28 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	Paolo Bonzini <pbonzini@...hat.com>,
	Eduardo Habkost <ehabkost@...hat.com>
Cc:	linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
	stable@...r.kernel.org
Subject: Re: [PATCH] KVM: SVM: fix trashing of MSR_TSC_AUX

On Wed, Jul 06, 2016 at 04:29:35PM +0200, Paolo Bonzini wrote:
> Can you test this in the meanwhile:
> 
>    git clone git://git.kernel.org/pub/scm/virt/kvm/kvm-unit-tests.git
>    cd kvm-unit-tests
>    ./configure
>    make
>    ./x86/run x86/tsc.flat -cpu kvm64,+rdtscp
> 
> On Intel I see:
> 
>    enabling apic
>    rdtsc latency 18
>    rdtsc after wrtsc(0): 727124155
>    rdtsc after wrtsc(100000000000): 100000001759
>    PASS: Test RDTSCP 0
>    PASS: Test RDTSCP 10
>    PASS: Test RDTSCP 256
>    SUMMARY: 3 tests

Ok, found it: I need to start the guest with "+rdtscp", see below.

Which begs the question: can we readd CPUID_EXT2_RDTSCP to the Opteron_*
models as in the second diff here:

https://lkml.kernel.org/r/20160706124438.GB7300@pd.tnic

?

Or are we still afraid of "host doesn't support requested feature"
messages from:

33b5e8c03ae7 ("target-i386: Disable rdtscp on Opteron_G* CPU models")

?

$ ./x86/run x86/tsc.flat -cpu kvm64,+rdtscp
qemu-system-x86_64 -enable-kvm -device pc-testdev -device isa-debug-exit,iobase=0xf4,iosize=0x4 -vnc none -serial stdio -device pci-testdev -kernel x86/tsc.flat -cpu kvm64,+rdtscp
enabling apic
rdtsc latency 68
rdtsc after wrtsc(0): 988590164
rdtsc after wrtsc(100000000000): 100000002807
PASS: Test RDTSCP 0
PASS: Test RDTSCP 10
PASS: Test RDTSCP 256

SUMMARY: 3 tests

latest qemu:

$ QEMU=/root/src/qemu/qemu.git/x86_64-softmmu/qemu-system-x86_64 ./x86/run x86/tsc.flat -cpu kvm64,+rdtscp
/root/src/qemu/qemu.git/x86_64-softmmu/qemu-system-x86_64 -enable-kvm -device pc-testdev -device isa-debug-exit,iobase=0xf4,iosize=0x4 -vnc none -serial stdio -device pci-testdev -kernel x86/tsc.flat -cpu kvm64,+rdtscp
enabling apic
rdtsc latency 69
rdtsc after wrtsc(0): 715310314
rdtsc after wrtsc(100000000000): 100000002434
PASS: Test RDTSCP 0
PASS: Test RDTSCP 10
PASS: Test RDTSCP 256

SUMMARY: 3 tests

guest booted *without* "+rdtscp":

taskset -c 3 ./rdtscp
aux1: 0x0
aux2: 0x0
p1: 284683839780, p2: 284684080314, 240534

with "+rdtscp":

$ taskset -c 3 ./rdtscp
aux1: 0x3
aux2: 0x3
p1: 168907589830, p2: 168907856068, 266238
$ taskset -c 2 ./rdtscp
aux1: 0x2
aux2: 0x2
p1: 176251144121, p2: 176251427089, 282968

Ok, all good.


-- 
Regards/Gruss,
    Boris.

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