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

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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>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
        "x86@...nel.org" <x86@...nel.org>, "hpa@...or.com" <hpa@...or.com>,
        "Lutomirski, Andy" <luto@...nel.org>,
        "Christopherson,, Sean" <seanjc@...gle.com>,
        "peterz@...radead.org" <peterz@...radead.org>,
        "Gross, Jurgen" <jgross@...e.com>,
        "Shankar, Ravi V" <ravi.v.shankar@...el.com>,
        "mhiramat@...nel.org" <mhiramat@...nel.org>,
        "andrew.cooper3@...rix.com" <andrew.cooper3@...rix.com>,
        "jiangshanlai@...il.com" <jiangshanlai@...il.com>
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