linux-kernel - Re: [PATCH] x86/paravirt: Fix build PARAVIRT_XXL=y without XEN

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Date:   Wed, 17 Nov 2021 15:33:20 -0800
From:   Dave Hansen <dave.hansen@...el.com>
To:     Sathyanarayanan Kuppuswamy 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        Borislav Petkov <bp@...en8.de>
Cc:     "Kirill A. Shutemov" <kirill@...temov.name>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        Andi Kleen <ak@...ux.intel.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Juergen Gross <jgross@...e.com>, Deep Shah <sdeep@...are.com>,
        "VMware, Inc." <pv-drivers@...are.com>
Subject: Re: [PATCH] x86/paravirt: Fix build PARAVIRT_XXL=y without XEN_PV

On 11/17/21 3:04 PM, Sathyanarayanan Kuppuswamy wrote:
> 1. Directly substitute TDVMCALLs in places where we require emulation.
...
> Since option#1 is not a scalable approach,

Why is this not "scalable"?  Just eyeballing the problem, here's my
laptop's kernel:

$ objdump  -d vmlinux | grep 'hlt ' | awk -F: '{print $1}' |  while read
addr; do  addr2line -e vmlinux $addr; done
arch/x86/include/asm/irqflags.h:51
arch/x86/include/asm/irqflags.h:51
arch/x86/include/asm/irqflags.h:57
arch/x86/include/asm/irqflags.h:57
arch/x86/include/asm/irqflags.h:57
arch/x86/include/asm/irqflags.h:57
arch/x86/include/asm/irqflags.h:51
arch/x86/include/asm/irqflags.h:51
arch/x86/include/asm/irqflags.h:51
arch/x86/kernel/fpu/init.c:84
arch/x86/include/asm/irqflags.h:57

There are a grand total of 3 sites from which a hlt originates.  With
only 11 possible instances and 3 sites to patch, I'm not sure anything
here needs to be "scalable".

I'd suspect half these sites aren't even reachable on a TDX system.