linux-kernel - Re: [PATCH v3 11/16] x86,hyperv: Clean up hv_do

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <aHXe_n8QNqxxgOBE@liuwe-devbox-ubuntu-v2.lamzopl0uupeniq2etz1fddiyg.xx.internal.cloudapp.net>
Date: Tue, 15 Jul 2025 04:54:22 +0000
From: Wei Liu <wei.liu@...nel.org>
To: Peter Zijlstra <peterz@...radead.org>
Cc: 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,
	hpa@...or.com, seanjc@...gle.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,
	Michael Kelley <mhklinux@...look.com>
Subject: Re: [PATCH v3 11/16] x86,hyperv: Clean up hv_do_hypercall()

On Mon, Jul 14, 2025 at 12:20:22PM +0200, Peter Zijlstra wrote:
> What used to be a simple few instructions has turned into a giant mess
> (for x86_64). Not only does it use static_branch wrong, it mixes it
> with dynamic branches for no apparent reason.
> 
> Notably it uses static_branch through an out-of-line function call,
> which completely defeats the purpose, since instead of a simple
> JMP/NOP site, you get a CALL+RET+TEST+Jcc sequence in return, which is
> absolutely idiotic.
> 
> Add to that a dynamic test of hyperv_paravisor_present, something
> which is set once and never changed.
> 
> Replace all this idiocy with a single direct function call to the
> right hypercall variant.
> 
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> Tested-by: Michael Kelley <mhklinux@...look.com>
> Reviewed-by: Michael Kelley <mhklinux@...look.com>

Acked-by: Wei Liu <wei.liu@...nel.org>