linux-kernel - Re: [PATCH v2 09/12] x86/msr: Use the alternatives mechanism for WRMSR

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: <fd98944e-52e4-4521-ae15-07f167b5dfbf@suse.com>
Date: Wed, 1 Oct 2025 11:13:19 +0200
From: Jürgen Groß <jgross@...e.com>
To: Sean Christopherson <seanjc@...gle.com>
Cc: linux-kernel@...r.kernel.org, x86@...nel.org, llvm@...ts.linux.dev,
 xin@...or.com, "H. Peter Anvin" <hpa@...or.com>,
 Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
 Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>,
 Nathan Chancellor <nathan@...nel.org>,
 Nick Desaulniers <nick.desaulniers+lkml@...il.com>,
 Bill Wendling <morbo@...gle.com>, Justin Stitt <justinstitt@...gle.com>
Subject: Re: [PATCH v2 09/12] x86/msr: Use the alternatives mechanism for
 WRMSR

On 30.09.25 18:00, Sean Christopherson wrote:
> On Tue, Sep 30, 2025, Juergen Gross wrote:
>> When available use one of the non-serializing WRMSR variants (WRMSRNS
>> with or without an immediate operand specifying the MSR register) in
>> __wrmsrq().
>>
>> For the safe/unsafe variants make __wrmsrq() to be a common base
>> function instead of duplicating the ALTERNATIVE*() macros. This
>> requires to let native_wrmsr() use native_wrmsrq() instead of
>> __wrmsrq(). While changing this, convert native_wrmsr() into an inline
>> function.
>>
>> Replace the only call of wsrmsrns() with the now equivalent call to
>> native_wrmsrq() and remove wsrmsrns().
>>
>> The paravirt case will be handled later.
> 
> ...
> 
>> @@ -268,21 +357,6 @@ static inline int wrmsrq_safe(u32 msr, u64 val)
>>   	return err;
>>   }
>>   
>> -/* Instruction opcode for WRMSRNS supported in binutils >= 2.40 */
>> -#define ASM_WRMSRNS _ASM_BYTES(0x0f,0x01,0xc6)
>> -
>> -/* Non-serializing WRMSR, when available.  Falls back to a serializing WRMSR. */
>> -static __always_inline void wrmsrns(u32 msr, u64 val)
> 
> FYI, a use of wrmsrns() is likely coming in through the KVM (x86) tree, commit
> 65391feb042b ("KVM: VMX: Add host MSR read/write helpers to consolidate preemption
> handling").

Thanks for the heads up!

> 
> Probably makes sense to spin v3 after the merge window?  Or on linux-next? (I
> can't tell what was used as the base, and I double-checked that the above commit
> is in linux-next).

I'll find a proper solution. :-)

Juergen

Download attachment "OpenPGP_0xB0DE9DD628BF132F.asc" of type "application/pgp-keys" (3684 bytes)

Download attachment "OpenPGP_signature.asc" of type "application/pgp-signature" (496 bytes)