LKML Archive on lore.kernel.org
help / color / mirror / Atom feed
From: "Raslan, KarimAllah" <karahmed@amazon.de>
To: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"kvm@vger.kernel.org" <kvm@vger.kernel.org>,
"pbonzini@redhat.com" <pbonzini@redhat.com>
Cc: "jmattson@google.com" <jmattson@google.com>,
"rkrcmar@redhat.com" <rkrcmar@redhat.com>
Subject: Re: [PATCH 1/2] X86/KVM: Properly restore 'tsc_offset' when running an L2 guest
Date: Thu, 12 Apr 2018 17:04:04 +0000 [thread overview]
Message-ID: <1523552643.32594.18.camel@amazon.de> (raw)
In-Reply-To: <d03d253a-d184-4c95-91b2-45e94659b9bd@redhat.com>
On Thu, 2018-04-12 at 18:35 +0200, Paolo Bonzini wrote:
> On 12/04/2018 17:12, KarimAllah Ahmed wrote:
> >
> > When the TSC MSR is captured while an L2 guest is running then restored,
> > the 'tsc_offset' ends up capturing the L02 TSC_OFFSET instead of the L01
> > TSC_OFFSET. So ensure that this is compensated for when storing the value.
> >
> > Cc: Jim Mattson <jmattson@google.com>
> > Cc: Paolo Bonzini <pbonzini@redhat.com>
> > Cc: Radim Krčmář <rkrcmar@redhat.com>
> > Cc: kvm@vger.kernel.org
> > Cc: linux-kernel@vger.kernel.org
> > Signed-off-by: KarimAllah Ahmed <karahmed@amazon.de>
> > ---
> > arch/x86/kvm/vmx.c | 12 +++++++++---
> > arch/x86/kvm/x86.c | 1 -
> > 2 files changed, 9 insertions(+), 4 deletions(-)
> >
> > diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> > index cff2f50..2f57571 100644
> > --- a/arch/x86/kvm/vmx.c
> > +++ b/arch/x86/kvm/vmx.c
> > @@ -2900,6 +2900,8 @@ static u64 guest_read_tsc(struct kvm_vcpu *vcpu)
> > */
> > static void vmx_write_tsc_offset(struct kvm_vcpu *vcpu, u64 offset)
> > {
> > + u64 l1_tsc_offset = 0;
> > +
> > if (is_guest_mode(vcpu)) {
> > /*
> > * We're here if L1 chose not to trap WRMSR to TSC. According
> > @@ -2908,16 +2910,20 @@ static void vmx_write_tsc_offset(struct kvm_vcpu *vcpu, u64 offset)
> > * to the newly set TSC to get L2's TSC.
> > */
> > struct vmcs12 *vmcs12;
> > +
> > /* recalculate vmcs02.TSC_OFFSET: */
> > vmcs12 = get_vmcs12(vcpu);
> > - vmcs_write64(TSC_OFFSET, offset +
> > - (nested_cpu_has(vmcs12, CPU_BASED_USE_TSC_OFFSETING) ?
> > - vmcs12->tsc_offset : 0));
> > +
> > + l1_tsc_offset = nested_cpu_has(vmcs12, CPU_BASED_USE_TSC_OFFSETING) ?
> > + vmcs12->tsc_offset : 0;
> > + vmcs_write64(TSC_OFFSET, offset + l1_tsc_offset);
> > } else {
> > trace_kvm_write_tsc_offset(vcpu->vcpu_id,
> > vmcs_read64(TSC_OFFSET), offset);
> > vmcs_write64(TSC_OFFSET, offset);
> > }
> > +
> > + vcpu->arch.tsc_offset = offset - l1_tsc_offset;
>
> Using both "offset + l1_tsc_offset" and "offset - l1_tsc_offset" in this
> function seems wrong to me: if vcpu->arch.tsc_offset must be "offset -
> l1_tsc_offset", then "offset" must be written to TSC_OFFSET.
Ooops! I forgot to remove the + l1_tsc_offset :D
>
> I think the bug was introduced by commit 3e3f50262. Before,
> vmx_read_tsc_offset returned the L02 offset; now it always contains the
> L01 offset. So the right fix is to adjust vcpu->arch.tsc_offset on
> nested vmentry/vmexit. If is_guest_mode(vcpu), kvm_read_l1_tsc must use
> a new kvm_x86_ops callback to subtract the L12 offset from the value it
> returns.
ack!
>
> Thanks,
>
> Paolo
>
> >
> > }
> >
> > /*
> > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> > index ac42c85..1a2ed92 100644
> > --- a/arch/x86/kvm/x86.c
> > +++ b/arch/x86/kvm/x86.c
> > @@ -1539,7 +1539,6 @@ EXPORT_SYMBOL_GPL(kvm_read_l1_tsc);
> > static void kvm_vcpu_write_tsc_offset(struct kvm_vcpu *vcpu, u64 offset)
> > {
> > kvm_x86_ops->write_tsc_offset(vcpu, offset);
> > - vcpu->arch.tsc_offset = offset;
> > }
> >
> > static inline bool kvm_check_tsc_unstable(void)
> >
>
>
Amazon Development Center Germany GmbH
Berlin - Dresden - Aachen
main office: Krausenstr. 38, 10117 Berlin
Geschaeftsfuehrer: Dr. Ralf Herbrich, Christian Schlaeger
Ust-ID: DE289237879
Eingetragen am Amtsgericht Charlottenburg HRB 149173 B
next prev parent reply other threads:[~2018-04-12 17:04 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-04-12 15:12 KarimAllah Ahmed
2018-04-12 15:12 ` [PATCH 2/2] kvm: nVMX: Introduce KVM_CAP_STATE KarimAllah Ahmed
2018-04-12 16:39 ` Paolo Bonzini
2018-04-14 15:56 ` Raslan, KarimAllah
2018-04-14 22:31 ` Raslan, KarimAllah
2018-04-16 16:22 ` Jim Mattson
2018-04-16 17:15 ` Raslan, KarimAllah
2018-04-26 22:28 ` Jim Mattson
2018-04-27 10:03 ` Paolo Bonzini
2018-04-27 15:19 ` Jim Mattson
2018-04-28 0:42 ` Paolo Bonzini
2018-04-12 16:35 ` [PATCH 1/2] X86/KVM: Properly restore 'tsc_offset' when running an L2 guest Paolo Bonzini
2018-04-12 17:04 ` Raslan, KarimAllah [this message]
2018-04-12 17:21 ` Raslan, KarimAllah
2018-04-12 20:21 ` Paolo Bonzini
2018-04-12 20:24 ` Raslan, KarimAllah
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=1523552643.32594.18.camel@amazon.de \
--to=karahmed@amazon.de \
--cc=jmattson@google.com \
--cc=kvm@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=pbonzini@redhat.com \
--cc=rkrcmar@redhat.com \
--subject='Re: [PATCH 1/2] X86/KVM: Properly restore '\''tsc_offset'\'' when running an L2 guest' \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).