On 2013-03-14 16:00, Gleb Natapov wrote:
> On Thu, Mar 14, 2013 at 03:52:11PM +0100, Jan Kiszka wrote:
>> vmx_vcpu_reset may now be called while already holding the srcu lock, so
>> we may overwrite what was already saved there. Also, we lock and unlock
>> in the same context, thus there was no need to save to the vcpu anyway.
>>
>> Signed-off-by: Jan Kiszka <jan.kiszka@xxxxxxxxxxx>
>> ---
>>
>> Marcelo just suggested this as the simplest fix for the issue caused by
>> the INIT/SIPI patch. Avoiding srcu lock for TSS handling might still be
>> possible but more tricky.
>>
>> arch/x86/kvm/vmx.c | 5 +++--
>> 1 files changed, 3 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
>> index 958ac3a..be5b1dc 100644
>> --- a/arch/x86/kvm/vmx.c
>> +++ b/arch/x86/kvm/vmx.c
>> @@ -4117,6 +4117,7 @@ static void vmx_vcpu_reset(struct kvm_vcpu *vcpu)
>> {
>> struct vcpu_vmx *vmx = to_vmx(vcpu);
>> u64 msr;
>> + int idx;
>>
>> vmx->rmode.vm86_active = 0;
>>
>> @@ -4190,9 +4191,9 @@ static void vmx_vcpu_reset(struct kvm_vcpu *vcpu)
>> vmcs_write16(VIRTUAL_PROCESSOR_ID, vmx->vpid);
>>
>> vmx->vcpu.arch.cr0 = X86_CR0_NW | X86_CR0_CD | X86_CR0_ET;
>> - vcpu->srcu_idx = srcu_read_lock(&vcpu->kvm->srcu);
>> + idx = srcu_read_lock(&vcpu->kvm->srcu);
>> vmx_set_cr0(&vmx->vcpu, kvm_read_cr0(vcpu)); /* enter rmode */
>> - srcu_read_unlock(&vcpu->kvm->srcu, vcpu->srcu_idx);
>> + srcu_read_unlock(&vcpu->kvm->srcu, idx);
> vmx_set_cr0() does:
> srcu_read_unlock(&vcpu->kvm->srcu, vcpu->srcu_idx);
> vmx_set_tss_addr(vcpu->kvm, 0xfeffd000);
> vcpu->srcu_idx = srcu_read_lock(&vcpu->kvm->srcu);
> So with this change the sequence will be:
>
> vcpu->srcu_idx = srcu_read_lock()
> idx = srcu_read_lock(&vcpu->kvm->srcu);
> srcu_read_unlock(&vcpu->kvm->srcu, vcpu->srcu_idx);
> vcpu->srcu_idx = srcu_read_lock(&vcpu->kvm->srcu);
> srcu_read_unlock(&vcpu->kvm->srcu, idx);
> srcu_read_unlock(&vcpu->kvm->srcu, vcpu->srcu_idx);
>
> Not sure this is valid.
Grmbl, likely not.
Jan
--
Siemens AG, Corporate Technology, CT RTC ITP SDP-DE
Corporate Competence Center Embedded Linux
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