Re: Setting nx bit in virtual CPU

[Richard Simpson <rs1002@huskydog.org.uk>]

On 08/04/10 08:23, Avi Kivity wrote:

> Strange.  Can you hack qemu-kvm's cpuid code where it issues the ioctl
> KVM_SET_CPUID2 to show what the data is?  I'm not where that code is in
> your version of qemu-kvm.

Gad, the last time I tried to mess around with this sort of low level
code was many years ago when I was a keen young bachelor burning the
midnight oil trying to get the weird IDE controller on my Alpha to work
properly!  Anyway, I have tried to give it a go.

I found a file called qemu-kvm-x86.c

It contained a function called kvm_setup_cpuid2 which I modified as follows:

int kvm_setup_cpuid2(CPUState *env, int nent,
                     struct kvm_cpuid_entry2 *entries)
{
        struct kvm_cpuid2 *cpuid;
        int r, i;
        fprintf(stderr, "cpuid=nent %d\n", nent);
        for (i=0; i < nent; i++) {
                fprintf(stderr, "%x %x %x %x %x %x %x\n",
entries[i].function, entries[i].index, entries[i].flags, entries[i].eax,
entries[i].ebx, entries[i].ecx, entries[i].edx);
                }
        cpuid = qemu_malloc(sizeof(*cpuid) + nent * sizeof(*entries));

        cpuid->nent = nent;
        memcpy(cpuid->entries, entries, nent * sizeof(*entries));
        r = kvm_vcpu_ioctl(env, KVM_SET_CPUID2, cpuid);
        free(cpuid);
        return r;
}

So, basically I go round a loop and print out the contents of each
kvm_cpuid_entry2 structure.

Results below, using Andre Przywara's handy nano-kernel.  I do hope that
some of this makes some kind of sense!

qemu-kvm -kernel cpuid_mb -vnc :0

cpuid=nent 21
40000000 0 0 0 4b4d564b 564b4d56 4d
40000001 0 0 7 0 0 0
0 0 0 4 68747541 444d4163 69746e65
1 0 0 623 800 80002001 78bfbfd
2 0 0 1 0 0 2c307d
3 0 0 0 0 0 0
4 0 1 121 1c0003f 3f 1
4 1 1 122 1c0003f 3f 1
4 2 1 143 3c0003f fff 1
4 3 1 0 0 0 0
80000000 0 0 8000000a 68747541 444d4163 69746e65
80000001 0 0 623 0 1 2181abfd
80000002 0 0 554d4551 72695620 6c617574 55504320
80000003 0 0 72657620 6e6f6973 312e3020 332e32
80000004 0 0 0 0 0 0
80000005 0 0 1ff01ff 1ff01ff 40020140 40020140
80000006 0 0 0 42004200 2008140 0
80000007 0 0 0 0 0 0
80000008 0 0 3028 0 0 0
80000009 0 0 0 0 0 0
8000000a 0 0 1 10 0 0

qemu-kvm -kernel cpuid_mb -cpu host -vnc :0

cpuid=nent 29
40000000 0 0 0 4b4d564b 564b4d56 4d
40000001 0 0 7 0 0 0
0 0 0 1 68747541 444d4163 69746e65
1 0 0 40ff2 800 80002001 78bfbff
80000000 0 0 80000018 68747541 444d4163 69746e65
80000001 0 0 40ff2 0 1 23c3fbff
80000002 0 0 20444d41 6c687441 74286e6f 3620296d
80000003 0 0 72502034 7365636f 20726f73 30303233
80000004 0 0 2b 0 0 0
80000005 0 0 1ff01ff 1ff01ff 40020140 40020140
80000006 0 0 0 42004200 2008140 0
80000007 0 0 0 0 0 0
80000008 0 0 3028 0 0 0
80000009 0 0 0 0 0 0
8000000a 0 0 1 10 0 0
8000000b 0 0 0 0 0 0
8000000c 0 0 0 0 0 0
8000000d 0 0 0 0 0 0
8000000e 0 0 0 0 0 0
8000000f 0 0 0 0 0 0
80000010 0 0 0 0 0 0
80000011 0 0 0 0 0 0
80000012 0 0 0 0 0 0
80000013 0 0 0 0 0 0
80000014 0 0 0 0 0 0
80000015 0 0 0 0 0 0
80000016 0 0 0 0 0 0
80000017 0 0 0 0 0 0
80000018 0 0 0 0 0 0

If I try with -no-kvm then nothing gets printed, presumably because this
is a kvm specific function and doesn't get called in that case.