linux-kernel - Re: [PATCH -tip] x86/locking/atomic: Use asm

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Message-ID: <Z8l922t-QoYGyuXq@gmail.com>
Date: Thu, 6 Mar 2025 11:50:03 +0100
From: Ingo Molnar <mingo@...nel.org>
To: Uros Bizjak <ubizjak@...il.com>
Cc: x86@...nel.org, linux-kernel@...r.kernel.org,
	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH -tip] x86/locking/atomic: Use asm_inline for atomic
 locking insns


* Ingo Molnar <mingo@...nel.org> wrote:

> Also, to shorten build & test times you can use the x86-64 defconfig. 
> It's a config more or less representative of what major distros 
> enable, and it's even bootable on some systems and in VMs, but it 
> builds in far less time.

And if your primary test method is KVM+Qemu, then the following build 
method will give you a representative core kernel bzImage that will 
boot most cloud VM images as-is:

  $ make -j128 ARCH=x86 defconfig kvm_guest.config bzImage

  $ ll arch/x86/boot/bzImage 
    -rw-rw-r-- 1 mingo mingo 13788160 Mar  6 11:42 arch/x86/boot/bzImage

And you can boot up a .raw distro image in an xterm:

  $ RAW=your_cloud_image.raw
  $ PARTUID=your_target_root_partition_UUID

  $ qemu-system-x86_64 \
   -enable-kvm \
   -smp cpus=4 \
   -m 2048 \
   -machine q35 \
   -cpu host \
   -global ICH9-LPC.disable_s3=1 \
   -net nic,model=virtio \
   -net user,hostfwd=tcp::8022-:22,hostfwd=tcp::8090-:80  \
   -drive "file=$RAW",if=none,format=raw,id=disk1 \
   -device virtio-blk-pci,drive=disk1,bootindex=1 \
   -serial mon:stdio \
   -nographic \
   -append "root=PARTUUID=$ID ro console=tty0 console=ttyS0,115200 earlyprintk=ttyS0,115200 consoleblank=0 ignore_loglevel" \
   -kernel arch/x86/boot/bzImage

This way you don't need any initrd build or modules nonsense - 
everything necessary is built in.

Bootable raw distro images can be found in numerous places, for example 
at:

  https://cloud.debian.org/images/cloud/bookworm-backports/

( And since I'm lazy to figure it out the 'cloud way', I usually read the 
  root UUID from the bootlog of the first unsuccessful attempt. )

Thanks,

	Ingo