lkml.org 
[lkml]   [2022]   [Jan]   [26]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
SubjectRe: [PATCH] KVM: nVMX: WARN on any attempt to allocate shadow VMCS for vmcs02
Date
Paolo Bonzini <pbonzini@redhat.com> writes:

> On 1/26/22 16:56, Vitaly Kuznetsov wrote:
>>> - WARN_ON(loaded_vmcs == &vmx->vmcs01 && loaded_vmcs->shadow_vmcs);
>>> + if (WARN_ON(loaded_vmcs != &vmx->vmcs01 || loaded_vmcs->shadow_vmcs))
>>> + return loaded_vmcs->shadow_vmcs;
>> Stupid question: why do we want to care about 'loaded_vmcs' at all,
>> i.e. why can't we hardcode 'vmx->vmcs01' in alloc_shadow_vmcs()? The
>> only caller is enter_vmx_operation() and AFAIU 'loaded_vmcs' will always
>> be pointing to 'vmx->vmcs01' (as enter_vmx_operation() allocates
>> &vmx->nested.vmcs02 so 'loaded_vmcs' can't point there!).
>>
>
> Well, that's why the WARN never happens. The idea is that if shadow
> VMCS _virtualization_ (not emulation, i.e. running L2 VMREAD/VMWRITE
> without even a vmexit to L0) was supported, then you would need a
> non-NULL shadow_vmcs in vmx->vmcs02.
>
> Regarding the patch, the old WARN was messy but it was also trying to
> avoid a NULL pointer dereference in the caller.
>
> What about:
>
> if (WARN_ON(loaded_vmcs->shadow_vmcs))
> return loaded_vmcs->shadow_vmcs;
>
> /* Go ahead anyway. */
> WARN_ON(loaded_vmcs != &vmx->vmcs01);
>
> ?
>

FWIW, this looks better [to my personal taste].

--
Vitaly

\
 
 \ /
  Last update: 2022-01-26 17:27    [W:0.060 / U:0.112 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site