From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jan Kiszka Subject: Re: [PATCH v2] KVM: VMX: Update instruction length on intercepted BP Date: Tue, 16 Feb 2010 09:05:40 +0100 Message-ID: <4B7A51D4.1040701@web.de> References: <4B795FD0.4060505@siemens.com> <20100216073352.GV2995@redhat.com> Mime-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="------------enigB0D25856D43D645D2FB09A86" Cc: Avi Kivity , Marcelo Tosatti , kvm To: Gleb Natapov Return-path: Received: from fmmailgate02.web.de ([217.72.192.227]:34389 "EHLO fmmailgate02.web.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932668Ab0BPIFm (ORCPT ); Tue, 16 Feb 2010 03:05:42 -0500 In-Reply-To: <20100216073352.GV2995@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: This is an OpenPGP/MIME signed message (RFC 2440 and 3156) --------------enigB0D25856D43D645D2FB09A86 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable Gleb Natapov wrote: > On Mon, Feb 15, 2010 at 03:53:04PM +0100, Jan Kiszka wrote: >> We intercept #BP while in guest debugging mode. As VM exits due to >> intercepted exceptions do not necessarily come with valid >> idt_vectoring, we have to update event_exit_inst_len explicitly in suc= h >> cases. At least in the absence of migration, this ensures that >> re-injections of #BP will find and use the correct instruction length.= >> > Thinking about it some more. Why do we exit to userspace at all if we > intercept wrong #DB? It seams to me not wise to have ability to inject > exceptions from userspace. Exceptions generation mechanism is a part of= > CPU and we shouldn't outsource part of CPU functionality to userspace. The guest debugging API was design to avoid maintaining a "countless" number of breakpoints in kernel space and instead chose to loop over user space to decide about #DB & #BP. So this part is required even if we start thinking about an alternative interface in the future. Jan >=20 >> Signed-off-by: Jan Kiszka >> --- >> >> Changes in v2: >> - added comments >> >> arch/x86/kvm/vmx.c | 13 +++++++++++++ >> 1 files changed, 13 insertions(+), 0 deletions(-) >> >> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c >> index f82b072..14873b9 100644 >> --- a/arch/x86/kvm/vmx.c >> +++ b/arch/x86/kvm/vmx.c >> @@ -2775,6 +2775,12 @@ static int handle_rmode_exception(struct kvm_vc= pu *vcpu, >> kvm_queue_exception(vcpu, vec); >> return 1; >> case BP_VECTOR: >> + /* >> + * Update instruction length as we may reinject the exception >> + * from user space while in guest debugging mode. >> + */ >> + to_vmx(vcpu)->vcpu.arch.event_exit_inst_len =3D >> + vmcs_read32(VM_EXIT_INSTRUCTION_LEN); >> if (vcpu->guest_debug & KVM_GUESTDBG_USE_SW_BP) >> return 0; >> /* fall through */ >> @@ -2897,6 +2903,13 @@ static int handle_exception(struct kvm_vcpu *vc= pu) >> kvm_run->debug.arch.dr7 =3D vmcs_readl(GUEST_DR7); >> /* fall through */ >> case BP_VECTOR: >> + /* >> + * Update instruction length as we may reinject #BP from >> + * user space while in guest debugging mode. Reading it for >> + * #DB as well causes no harm, it is not used in that case. >> + */ >> + vmx->vcpu.arch.event_exit_inst_len =3D >> + vmcs_read32(VM_EXIT_INSTRUCTION_LEN); >> kvm_run->exit_reason =3D KVM_EXIT_DEBUG; >> kvm_run->debug.arch.pc =3D vmcs_readl(GUEST_CS_BASE) + rip; >> kvm_run->debug.arch.exception =3D ex_no; >=20 > -- > Gleb. --------------enigB0D25856D43D645D2FB09A86 Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.9 (GNU/Linux) Comment: Using GnuPG with SUSE - http://enigmail.mozdev.org iEYEARECAAYFAkt6UdQACgkQitSsb3rl5xTvVACfVoWDhF9CGigKqvHjo0Y9by5O MIwAnA/qKwE8SDwry7N9AEyK98lPoFGe =KtAW -----END PGP SIGNATURE----- --------------enigB0D25856D43D645D2FB09A86--