linux-kernel - Re: [PATCH v2 00/13] objtool: Detect and warn about indirect calls in _

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Message-ID: <20250502084007.GS4198@noisy.programming.kicks-ass.net>
Date: Fri, 2 May 2025 10:40:07 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Sean Christopherson <seanjc@...gle.com>
Cc: "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org, kys@...rosoft.com,
	haiyangz@...rosoft.com, wei.liu@...nel.org, decui@...rosoft.com,
	tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
	dave.hansen@...ux.intel.com, pbonzini@...hat.com, ardb@...nel.org,
	kees@...nel.org, Arnd Bergmann <arnd@...db.de>,
	gregkh@...uxfoundation.org, jpoimboe@...nel.org,
	linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org,
	kvm@...r.kernel.org, linux-efi@...r.kernel.org,
	samitolvanen@...gle.com, ojeda@...nel.org, xin@...or.com
Subject: Re: [PATCH v2 00/13] objtool: Detect and warn about indirect calls
 in __nocfi functions

On Thu, May 01, 2025 at 11:30:18AM -0700, Sean Christopherson wrote:

> Uh, aren't you making this way more complex than it needs to be? 

Possibly :-)

> IIUC, KVM never
> uses the FRED hardware entry points, i.e. the FRED entry tables don't need to be
> in place because they'll never be used.  The only bits of code KVM needs is the
> __fred_entry_from_kvm() glue.

But __fred_entry_from_kvm() calls into fred_extint(), which then
directly uses the fred sysvec_table[] for dispatch. How would we not
have to set up that table?

> Lightly tested, but this combo works for IRQs and NMIs on non-FRED hardware.

So the FRED NMI code is significantly different from the IDT NMI code
and I really didn't want to go mixing those.

If we get a nested NMI I don't think it'll behave well.