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RE: [PATCH v10 36/38] x86/fred: Add fred_syscall_init()
- To: Thomas Gleixner <tglx@xxxxxxxxxxxxx>, "linux-doc@xxxxxxxxxxxxxxx" <linux-doc@xxxxxxxxxxxxxxx>, "linux-kernel@xxxxxxxxxxxxxxx" <linux-kernel@xxxxxxxxxxxxxxx>, "linux-edac@xxxxxxxxxxxxxxx" <linux-edac@xxxxxxxxxxxxxxx>, "linux-hyperv@xxxxxxxxxxxxxxx" <linux-hyperv@xxxxxxxxxxxxxxx>, "kvm@xxxxxxxxxxxxxxx" <kvm@xxxxxxxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- From: "Li, Xin3" <xin3.li@xxxxxxxxx>
- Date: Wed, 20 Sep 2023 04:33:38 +0000
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- Delivery-date: Wed, 20 Sep 2023 04:34:11 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
- Thread-index: AQHZ5strXMSQ17oxYk2by6W1B7FxqLAh2QeAgAFNrPA=
- Thread-topic: [PATCH v10 36/38] x86/fred: Add fred_syscall_init()
> > +static inline void fred_syscall_init(void) {
> > + /*
> > + * Per FRED spec 5.0, FRED uses the ring 3 FRED entrypoint for SYSCALL
> > + * and SYSENTER, and ERETU is the only legit instruction to return to
> > + * ring 3, as a result there is _no_ need to setup the SYSCALL and
> > + * SYSENTER MSRs.
> > + *
> > + * Note, both sysexit and sysret cause #UD when FRED is enabled.
> > + */
> > + wrmsrl(MSR_LSTAR, 0ULL);
> > + wrmsrl_cstar(0ULL);
>
> That write is pointless. See the comment in wrmsrl_cstar().
What I heard is that AMD is going to support FRED.
Both LSTAR and CSTAR have no function when FRED is enabled, so maybe
just do NOT write to them?
Thanks!
Xin
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