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Date: Mon, 10 Sep 2012 14:15:49 +0200
From: Paolo Bonzini <pbonzini@redhat.com>
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Subject: Re: [Qemu-devel] memtest 4.20+ does not work with -cpu host
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To: Peter Lieven <pl@dlhnet.de>
Cc: Avi Kivity <avi@redhat.com>, "kvm@vger.kernel.org" <kvm@vger.kernel.org>, "qemu-devel@nongnu.org" <qemu-devel@nongnu.org>

Il 10/09/2012 13:52, Peter Lieven ha scritto:
>> dd if=/dev/cpu/0/msr skip=$((0x194)) bs=8 count=1 | xxd
>> dd if=/dev/cpu/0/msr skip=$((0xCE)) bs=8 count=1 | xxd
> it only works without the skip. but the msr device returns all zeroes.

Hmm, the strange API of the MSR device doesn't work well with dd (dd
skips to 0x194 * 8 because bs is 8.  You can try this program:

#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>

int rdmsr(int fd, long reg)
{
    char msg[40];
    long long val;
    sprintf(msg, "rdmsr(%#x)", reg);
    if (pread(fd, &val, 8, reg) < 0) {
        perror(msg);
    } else {
        printf("%s: %#016llx\n", msg, val);
        fflush(stdout);
    }
}


int main()
{
    int fd = open("/dev/cpu/0/msr", O_RDONLY);
    if (fd < 0) { perror("open"); exit(1); }
    rdmsr(fd, 0x194);
    rdmsr(fd, 0xCE);
}

Paolo