linux-kernel - Re: [PATCH v1 3/3] x86/msr: Convert a native_wrmsr() use to native

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: <b8f741d6-47a1-4cc8-a5b2-45ee86fcb773@zytor.com>
Date: Fri, 16 May 2025 21:42:42 -0700
From: Xin Li <xin@...or.com>
To: Ingo Molnar <mingo@...nel.org>
Cc: linux-kernel@...r.kernel.org, xen-devel@...ts.xenproject.org,
        linux-acpi@...r.kernel.org, tglx@...utronix.de, bp@...en8.de,
        dave.hansen@...ux.intel.com, x86@...nel.org, hpa@...or.com,
        peterz@...radead.org, jgross@...e.com, boris.ostrovsky@...cle.com,
        rafael@...nel.org, lenb@...nel.org
Subject: Re: [PATCH v1 3/3] x86/msr: Convert a native_wrmsr() use to
 native_wrmsrq()

On 5/15/2025 10:54 AM, Xin Li wrote:
> On 5/15/2025 8:27 AM, Ingo Molnar wrote:
>>
>> * Xin Li (Intel) <xin@...or.com> wrote:
>>
>>> Convert a native_wrmsr() use to native_wrmsrq() to zap meaningless type
>>> conversions when a u64 MSR value is splitted into two u32.
>>>
>>
>> BTW., at this point we should probably just replace
>> sev_es_wr_ghcb_msr() calls with direct calls to:
>>
>>     native_wrmsrq(MSR_AMD64_SEV_ES_GHCB, ...);
>>
>> as sev_es_wr_ghcb_msr() is now basically an open-coded native_wrmsrq().
>>
> 
> I thought about it, however it looks to me that current code prefers not
> to spread MSR_AMD64_SEV_ES_GHCB in 17 callsites.  And anyway it's a 
> __always_inline function.
> 
> But as you have asked, I will make the change unless someone objects.

Hi Ingo,

I took a further look and found that we can't simply replace
sev_es_wr_ghcb_msr() with native_wrmsrq(MSR_AMD64_SEV_ES_GHCB, ...).

There are two sev_es_wr_ghcb_msr() definitions.  One is defined in
arch/x86/boot/compressed/sev.h and it references boot_wrmsr() defined in
arch/x86/boot/msr.h to do MSR write.

The other one is defined in arch/x86/include/asm/sev-internal.h, which
uses native_wrmsrq() from arch/x86/include/asm/msr.h to write MSR.

Because:
1) arch/x86/boot/startup/sev-shared.c is included in both
         arch/x86/boot/compressed/sev.c
    and
         arch/x86/boot/startup/sev-startup.c

2) arch/x86/boot/startup/sev-shared.c has several references to
    sev_es_wr_ghcb_msr(),

sev_es_wr_ghcb_msr() is converted to boot_wrmsr() when included in
arch/x86/boot/compressed/sev.c or native_wrmsrq() when included in
arch/x86/boot/startup/sev-startup.c.

It would change the compressed code to use native_wrmsrq() if we remove
sev_es_wr_ghcb_msr() from arch/x86/include/asm/sev-internal.h and use 
native_wrmsrq() directly in the startup code.

We probably should get rid of boot_wrmsr() and use native_wrmsrq() in
the compressed code because they are indeed the same thing.  But as we
are so close to the v6.16 merge window, I don't think it's a good idea
to make the change right now.

So maybe I should just drop this patch and we can do the job after the 
coming merge window.

But if you think it's not a bad idea to replace native_wrmsr() with
native_wrmsrq() right now, I can keep this original patch.

Thanks!
     Xin