linux-kernel - RE: [PATCH v10 33/38] x86/entry: Add fred_entry_from

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Message-ID: <SA1PR11MB6734FED6128A0D32243DB118A8F9A@SA1PR11MB6734.namprd11.prod.outlook.com>
Date:   Wed, 20 Sep 2023 23:10:23 +0000
From:   "Li, Xin3" <xin3.li@...el.com>
To:     Paolo Bonzini <pbonzini@...hat.com>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-edac@...r.kernel.org" <linux-edac@...r.kernel.org>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "xen-devel@...ts.xenproject.org" <xen-devel@...ts.xenproject.org>
CC:     "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "bp@...en8.de" <bp@...en8.de>,
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Subject: RE: [PATCH v10 33/38] x86/entry: Add fred_entry_from_kvm() for VMX to
 handle IRQ/NMI

> > +	/*
> > +	 * Don't check the FRED stack level, the call stack leading to this
> > +	 * helper is effectively constant and shallow (relatively speaking).
> 
> It's more that we don't need to protect from reentrancy.  The external
> interrupt uses stack level 0 so no adjustment would be needed anyway,
> and NMI does not use an IST even in the non-FRED case.

I will incorporate this comment.

I think a VMX NMI is kind of like a user level NMI, and we don't need
to worry about nested NMIs.

> 
> > +	 * Emulate the FRED-defined redzone and stack alignment.
> > +	 */
> > +	sub $(FRED_CONFIG_REDZONE_AMOUNT << 6), %rsp
> > +	and $FRED_STACK_FRAME_RSP_MASK, %rsp