Xen project Mailing List

Re: [Xen-devel] [PATCH] pvh: Fix regression caused by assumption that HVM paths MUST use io-backend device.

From: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>

Date: Tue, 4 Feb 2014 11:42:58 -0500

Cc: george.dunlap@xxxxxxxxxxxxx, Konrad Rzeszutek Wilk <konrad@xxxxxxxxxx>, jun.nakajima@xxxxxxxxx, yang.z.zhang@xxxxxxxxx, xen-devel@xxxxxxxxxxxxxxxxxxxx

Delivery-date: Tue, 04 Feb 2014 16:44:19 +0000

List-id: Xen developer discussion <xen-devel.lists.xen.org>

On Tue, Feb 04, 2014 at 03:46:48PM +0000, Jan Beulich wrote: > >>> On 04.02.14 at 16:32, Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx> > >>> wrote: > > On Tue, Feb 04, 2014 at 03:02:44PM +0000, Jan Beulich wrote: > >> Wasn't it that Mukesh's patch simply was yours with the two > >> get_ioreq()s folded by using a local variable? > > > > Yes. As so > > Thanks. Except that ... > > > --- a/xen/arch/x86/hvm/vmx/vvmx.c > > +++ b/xen/arch/x86/hvm/vmx/vvmx.c > > @@ -1394,13 +1394,13 @@ void nvmx_switch_guest(void) > > struct vcpu *v = current; > > struct nestedvcpu *nvcpu = &vcpu_nestedhvm(v); > > struct cpu_user_regs *regs = guest_cpu_user_regs(); > > - > > + ioreq_t *p = get_ioreq(v); > > ... you don't want to drop the blank line, and naming the new > variable "ioreq" would seem preferable. > > > /* > > * a pending IO emualtion may still no finished. In this case, > > * no virtual vmswith is allowed. Or else, the following IO > > * emulation will handled in a wrong VCPU context. > > */ > > - if ( get_ioreq(v)->state != STATE_IOREQ_NONE ) > > + if ( p && p->state != STATE_IOREQ_NONE ) > > And, as said before, I'd think "!p ||" instead of "p &&" would be > the right thing here. Yang, Jun? I have two patches - one the simpler one that is pretty straightfoward and the one you suggested. Either one fixes PVH guests. I also did bootup tests with HVM guests to make sure they worked. Attached and inline. From 47a5554201f0bc1778e5bcbde8c39088707f727f Mon Sep 17 00:00:00 2001 From: Mukesh Rathor <mukesh.rathor@xxxxxxxxxx> Date: Mon, 3 Feb 2014 11:45:52 -0500 Subject: [PATCH] pvh: Fix regression caused by assumption that HVM paths MUST use io-backend device. The commit 09bb434748af9bfe3f7fca4b6eef721a7d5042a4 "Nested VMX: prohibit virtual vmentry/vmexit during IO emulation" assumes that the HVM paths are only taken by HVM guests. With the PVH enabled that is no longer the case - which means that we do not have to have the IO-backend device (QEMU) enabled. As such, that patch can crash the hypervisor: Xen call trace: [<ffff82d0801ddd9a>] nvmx_switch_guest+0x4d/0x903 [<ffff82d0801de95b>] vmx_asm_vmexit_handler+0x4b/0xc0 Pagetable walk from 000000000000001e: L4[0x000] = 0000000000000000 ffffffffffffffff **************************************** Panic on CPU 7: FATAL PAGE FAULT [error_code=0000] Faulting linear address: 000000000000001e **************************************** as we do not have an io based backend. CC: Yang Zhang <yang.z.zhang@xxxxxxxxx> CC: Jun Nakajima <jun.nakajima@xxxxxxxxx> Signed-off-by: Mukesh Rathor <mukesh.rathor@xxxxxxxxxx> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx> --- xen/arch/x86/hvm/vmx/vvmx.c | 3 ++- 1 files changed, 2 insertions(+), 1 deletions(-) diff --git a/xen/arch/x86/hvm/vmx/vvmx.c b/xen/arch/x86/hvm/vmx/vvmx.c index d2ba435..563b02f 100644 --- a/xen/arch/x86/hvm/vmx/vvmx.c +++ b/xen/arch/x86/hvm/vmx/vvmx.c @@ -1394,13 +1394,14 @@ void nvmx_switch_guest(void) struct vcpu *v = current; struct nestedvcpu *nvcpu = &vcpu_nestedhvm(v); struct cpu_user_regs *regs = guest_cpu_user_regs(); + ioreq_t *ioreq = get_ioreq(v); /* * a pending IO emualtion may still no finished. In this case, * no virtual vmswith is allowed. Or else, the following IO * emulation will handled in a wrong VCPU context. */ - if ( get_ioreq(v)->state != STATE_IOREQ_NONE ) + if ( ioreq && ioreq->state != STATE_IOREQ_NONE ) return; /* * a softirq may interrupt us between a virtual vmentry is -- 1.7.7.6 From d76fc0d2f59ac65bd692adfa5f215da9ecf85d6a Mon Sep 17 00:00:00 2001 From: Mukesh Rathor <mukesh.rathor@xxxxxxxxxx> Date: Mon, 3 Feb 2014 11:45:52 -0500 Subject: [PATCH] pvh: Fix regression due to assumption that HVM paths MUST use io-backend device. The commit 09bb434748af9bfe3f7fca4b6eef721a7d5042a4 "Nested VMX: prohibit virtual vmentry/vmexit during IO emulation" assumes that the HVM paths are only taken by HVM guests. With the PVH enabled that is no longer the case - which means that we do not have to have the IO-backend device (QEMU) enabled. As such, that patch can crash the hypervisor: Xen call trace: [<ffff82d0801ddd9a>] nvmx_switch_guest+0x4d/0x903 [<ffff82d0801de95b>] vmx_asm_vmexit_handler+0x4b/0xc0 Pagetable walk from 000000000000001e: L4[0x000] = 0000000000000000 ffffffffffffffff **************************************** Panic on CPU 7: FATAL PAGE FAULT [error_code=0000] Faulting linear address: 000000000000001e **************************************** as we do not have an io based backend. In the case that the PVH guest does run an HVM guest inside it - we need to do further work to suport this - and for now the check will bail us out. We also fix spelling mistakes and the sentence structure. CC: Yang Zhang <yang.z.zhang@xxxxxxxxx> CC: Jun Nakajima <jun.nakajima@xxxxxxxxx> Suggested-by: Jan Beulich <JBeulich@xxxxxxxx> Signed-off-by: Mukesh Rathor <mukesh.rathor@xxxxxxxxxx> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx> --- xen/arch/x86/hvm/vmx/vvmx.c | 10 +++++++--- 1 files changed, 7 insertions(+), 3 deletions(-) diff --git a/xen/arch/x86/hvm/vmx/vvmx.c b/xen/arch/x86/hvm/vmx/vvmx.c index d2ba435..71522cf 100644 --- a/xen/arch/x86/hvm/vmx/vvmx.c +++ b/xen/arch/x86/hvm/vmx/vvmx.c @@ -1394,13 +1394,17 @@ void nvmx_switch_guest(void) struct vcpu *v = current; struct nestedvcpu *nvcpu = &vcpu_nestedhvm(v); struct cpu_user_regs *regs = guest_cpu_user_regs(); + ioreq_t *ioreq = get_ioreq(v); /* - * a pending IO emualtion may still no finished. In this case, + * A pending IO emulation may still be not finished. In this case, * no virtual vmswith is allowed. Or else, the following IO - * emulation will handled in a wrong VCPU context. + * emulation will be handled in a wrong VCPU context. If there are + * no IO backends - PVH guest by itself or a PVH guest with an HVM guest + * running inside - we don't want to continue as this setup is not + * implemented nor supported as of right now. */ - if ( get_ioreq(v)->state != STATE_IOREQ_NONE ) + if ( !ioreq || ioreq->state != STATE_IOREQ_NONE ) return; /* * a softirq may interrupt us between a virtual vmentry is -- 1.7.7.6 > > Jan >

_______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel

©2013 Xen Project, A Linux Foundation Collaborative Project. All Rights Reserved.
Linux Foundation is a registered trademark of The Linux Foundation.
Xen Project is a trademark of The Linux Foundation.