Date: Wed, 21 Feb 2018 20:08:34 +0100 From: "Fabian Freyer" <fabian.freyer@physik.tu-berlin.de> To: "Peter Grehan" <grehan@freebsd.org> Cc: freebsd-virtualization@freebsd.org Subject: Re: VMX exit reason=33 and general userboot.so questions Message-ID: <5C51D1DD-BD11-40BD-B2EB-185524774D2C@physik.tu-berlin.de> In-Reply-To: <0142d062-ca13-6917-bb06-28cac727680b@freebsd.org> References: <BA57D57B-08B0-45DB-B200-C5C31994AAC7@physik.tu-berlin.de> <0142d062-ca13-6917-bb06-28cac727680b@freebsd.org>
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Hi Peter,
thanks for your response!
On 21 Feb 2018, at 17:59, Peter Grehan wrote:
> > exit_reason 33
>
> From the Intel SDM, vol 3B Appendix C, this error is "VM-entry failure=
due to invalid guest state".
Yes, I=E2=80=99m currently going through SDM, vol 3B, section 26.3, and
> These errors can be difficult to debug given the large amount of guest=
state involved :(
definitely accurately describes the experience. That said, I=E2=80=99m go=
ing through each check and trying to see what is going wrong.
> However, looking at the state from your dump:
>
> > tr desc[0] 0x0000000000000000/0x00000000/0x00000000
>
> I believe you will have to set this. Here's the comment and relevant c=
ode fragment from grub2-bhyve grub-core/kern/emu/bhyve_hostif.c:grub_emu_=
bhyve_boot32()
>
> /*
> * XXX TR is pointing to null selector even though we set the
> * TSS segment to be usable with a base address and limit of 0.
> * Has to be 8b or vmenter will fail
> */
> desc_access =3D 0x0000008b;
> assert(vm_set_desc(bhyve_ctx, 0, VM_REG_GUEST_TR, 0x1000, 0x67,
> desc_access) =3D=3D 0);
>
> grub2-bhyve has been able to load/boot multiboot images, so I suspect =
the register settings in grub_emu_bhyve_boot32() are a good place to star=
t from.
Thanks. I=E2=80=99ve tried setting all registers (especially) the segment=
registers as grub2-bhyve does, but I still don=E2=80=99t seem to be able=
to boot correctly. Fixing the TR descriptor didn=E2=80=99t do it.
Here=E2=80=99s a list of the descriptors I set up:
ds desc[0] 0x0000000000000000/0xffffffff/0x00000093
es desc[0] 0x0000000000000000/0xffffffff/0x00000093
fs desc[0] 0x0000000000000000/0xffffffff/0x00000093
gs desc[0] 0x0000000000000000/0xffffffff/0x00000093
ss desc[0] 0x0000000000000000/0xffffffff/0x00000093
cs desc[0] 0x0000000000000000/0xffffffff/0x0000009b
tr desc[0] 0x0000000000001000/0x00000067/0x0000008b
ldtr desc[0] 0x0000000000000000/0x0000ffff/0x00010082
gdtr points to a default gdt as set up in grub2-bhyve:
static uint16_t bhyve_gdt[] =3D {
0x0000, 0x0000, 0x0000, 0x0000, /* Null */
0x0000, 0x0000, 0x0000, 0x0000, /* Null #2 */
0xffff, 0x0000, 0x9a00, 0x00cf, /* code */
0xffff, 0x0000, 0x9200, 0x00cf, /* data */
0x0000, 0x0000, 0x8900, 0x0080 /* tss */
};
gdtr[0] 0x0000000000100161/0x00000027
idtr[0] 0x0000000000000000/0x00000000
The rest is set up as by grub2-bhyve:
cs[0] 0x0008
ds[0] 0x0010
es[0] 0x0010
fs[0] 0x0010
gs[0] 0x0010
ss[0] 0x0010
tr[0] 0x0000
ldtr[0] 0x0000
I=E2=80=99m assuming entry_ctls[0] =3D 0x91fb is the VM-entry control, bu=
t is it the value described by Table 24-7 of the SDM Volume 3B? Is this c=
onstant for the first entry after running bhyveload? That is, when writi=
ng some compliance checks against section 26.3.1, can I just hardcode tha=
t value?
I=E2=80=99m starting to dig through the bhyverun code, but I=E2=80=99m st=
ill pretty new to VMX stuff, so I am ending up with more questions than a=
nswers.
Fabian
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