From 03c71cda215fd9183a0fe10cb42394d63e3879c5 Mon Sep 17 00:00:00 2001 From: George Dunlap Date: Fri, 20 Jul 2018 16:04:01 +0100 Subject: [PATCH] x86/altp2m: Make sure EPTP_INDEX is up-to-date when enabling #VE vmx_vmexit_handler() assumes that if SECONDARY_EXEC_ENABLE_VIRT_EXCEPTIONS is set, that the value in EPTP_INDEX is valid. Unfortunately, the function which sets this bit (vmx_vcpu_update_vmfunc_ve) doesn't actually set EPTP_INDEX; it will only be set the next time vmx_vcpu_update_eptp() is called. This means that if a vcpu makes a vmexit between these two points, the EPTP_INDEX it reads will be invalid. The first time this race happens for a domain, EPTP_INDEX will most likely be zero, which is the index for the "host" p2m -- and thus is often correct. But the second time this race happens, the value will typically be INVALID_ALTP2M, which will hit the following BUG: BUG_ON(idx >= MAX_ALTP2M); Worse, if for some reason the current altp2m was *not* `0` during this window (say, because a toolstack changed the VM to a different view), then the accounting of active vcpus for an altp2m will be thrown off. Fix this by always updating EPTP_INDEX to the current altp2m index when enabling #VE. Reported-by: Razvan Cojocaru Signed-off-by: George Dunlap --- xen/arch/x86/hvm/vmx/vmx.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/xen/arch/x86/hvm/vmx/vmx.c b/xen/arch/x86/hvm/vmx/vmx.c index bcf95f9a5f..bc25daed2c 100644 --- a/xen/arch/x86/hvm/vmx/vmx.c +++ b/xen/arch/x86/hvm/vmx/vmx.c @@ -2191,7 +2191,14 @@ static void vmx_vcpu_update_vmfunc_ve(struct vcpu *v) mfn = get_gfn_query_unlocked(d, gfn_x(vcpu_altp2m(v).veinfo_gfn), &t); if ( !mfn_eq(mfn, INVALID_MFN) ) + { __vmwrite(VIRT_EXCEPTION_INFO, mfn_x(mfn) << PAGE_SHIFT); + /* + * Make sure we have an up-to-date EPTP_INDEX when + * setting SECONDARY_EXEC_ENABLE_VIRT_EXCEPTIONS + */ + __vmwrite(EPTP_INDEX, vcpu_altp2m(v).p2midx); + } else v->arch.hvm_vmx.secondary_exec_control &= ~SECONDARY_EXEC_ENABLE_VIRT_EXCEPTIONS; -- 2.18.0