On 2013-03-04 15:15, Gleb Natapov wrote:
> On Mon, Mar 04, 2013 at 03:09:51PM +0100, Jan Kiszka wrote:
>> On 2013-03-04 14:22, Gleb Natapov wrote:
>>> On Thu, Feb 28, 2013 at 10:44:47AM +0100, Jan Kiszka wrote:
>>>> The logic for calculating the value with which we call kvm_set_cr0/4 was
>>>> broken (will definitely be visible with nested unrestricted guest mode
>>>> support). Also, we performed the check regarding CR0_ALWAYSON too early
>>>> when in guest mode.
>>>>
>>>> What really needs to be done on both CR0 and CR4 is to mask out L1-owned
>>>> bits and merge them in from GUEST_CR0/4. In contrast, arch.cr0/4 and
>>>> arch.cr0/4_guest_owned_bits contain the mangled L0+L1 state and, thus,
>>>> are not suited as input.
>>>>
>>>> For both CRs, we can then apply the check against VMXON_CRx_ALWAYSON and
>>>> refuse the update if it fails. To be fully consistent, we implement this
>>>> check now also for CR4.
>>>>
>>>> Finally, we have to set the shadow to the value L2 wanted to write
>>>> originally.
>>>>
>>>> Signed-off-by: Jan Kiszka <jan.kiszka@xxxxxxxxxxx>
>>>> ---
>>>>
>>>> Found while making unrestricted guest mode working. Not sure what impact
>>>> the bugs had on current feature level, if any.
>>>>
>>>> For interested folks, I've pushed my nEPT environment here:
>>>>
>>>> git://git.kiszka.org/linux-kvm.git nept-hacking
>>>>
>>>> arch/x86/kvm/vmx.c | 49 ++++++++++++++++++++++++++++++-------------------
>>>> 1 files changed, 30 insertions(+), 19 deletions(-)
>>>>
>>>> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
>>>> index 7cc566b..d1dac08 100644
>>>> --- a/arch/x86/kvm/vmx.c
>>>> +++ b/arch/x86/kvm/vmx.c
>>>> @@ -4605,37 +4605,48 @@ vmx_patch_hypercall(struct kvm_vcpu *vcpu, unsigned char *hypercall)
>>>> /* called to set cr0 as appropriate for a mov-to-cr0 exit. */
>>>> static int handle_set_cr0(struct kvm_vcpu *vcpu, unsigned long val)
>>>> {
>>>> - if (to_vmx(vcpu)->nested.vmxon &&
>>>> - ((val & VMXON_CR0_ALWAYSON) != VMXON_CR0_ALWAYSON))
>>>> - return 1;
>>>> -
>>>> if (is_guest_mode(vcpu)) {
>>>> - /*
>>>> - * We get here when L2 changed cr0 in a way that did not change
>>>> - * any of L1's shadowed bits (see nested_vmx_exit_handled_cr),
>>>> - * but did change L0 shadowed bits. This can currently happen
>>>> - * with the TS bit: L0 may want to leave TS on (for lazy fpu
>>>> - * loading) while pretending to allow the guest to change it.
>>>> - */
>>> Can't say I understand this patch yet, but it looks like the comment is
>>> still valid. Why have you removed it?
>>
>> L0 allows L1 or L2 at most to own TS, the rest is host-owned. I think
>> the comment was always misleading.
>>
> I do not see how it is misleading. For everything but TS we will not get
> here (if L1 is kvm). For TS we will get here if L1 allows L2 to change
> it, but L0 does not.
For everything *but guest-owned* we will get here, thus for most CR0
accesses (bit-wise, not regarding frequency).
Jan
--
Siemens AG, Corporate Technology, CT RTC ITP SDP-DE
Corporate Competence Center Embedded Linux
--
To unsubscribe from this list: send the line "unsubscribe kvm" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
