Re: [Xen-devel] [PATCH for-4.12 V3] x86/altp2m: fix HVMOP_altp2m_set_domain_state race

[Razvan Cojocaru <rcojocaru@xxxxxxxxxxxxxxx>]

On 2/11/19 6:59 PM, Jan Beulich wrote:
> Plus I can't see p2m_switch_vcpu_altp2m_by_id() called for
> any HVMOP_altp2m_* at all. One of the actual callers is guarded
> by altp2m_active(), but the other isn't.
Actually I see that both places are guarded by altp2m_active().

In p2m.c we have:

2312 void p2m_altp2m_check(struct vcpu *v, uint16_t idx)
2313 {
2314     if ( altp2m_active(v->domain) )
2315         p2m_switch_vcpu_altp2m_by_id(v, idx);
2316 }

and in vmx.c:

2225 static int vmx_vcpu_emulate_vmfunc(const struct cpu_user_regs *regs)
2226 {
2227     int rc = X86EMUL_EXCEPTION;
2228     struct vcpu *curr = current;
2229
2230     if ( !cpu_has_vmx_vmfunc && altp2m_active(curr->domain) &&
2231          regs->eax == 0 &&
2232          p2m_switch_vcpu_altp2m_by_id(curr, regs->ecx) )
2233         rc = X86EMUL_OKAY;
2234
2235     return rc;
2236 }

here there's an "&& altp2m_active(curr->domain)" in the if().

So I suppose in our scenario all that's needed it a similar check here:

4636     case HVMOP_altp2m_switch_p2m:
4637         rc = p2m_switch_domain_altp2m_by_id(d, a.u.view.view);
4638         break;

for the other function, p2m_switch_domain_altp2m_by_id().

Unless I'm missing something.


Thanks,
Razvan

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