linux-kernel - Re: [RFC PATCH 1/2] x86, lib, xenpv: Add WBNOINVD helper functions

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: <bc4a4095-d8bd-4d97-a623-be35ef81aad0@zytor.com>
Date: Mon, 2 Dec 2024 20:09:49 -0800
From: Xin Li <xin@...or.com>
To: Kevin Loughlin <kevinloughlin@...gle.com>,
        Andrew Cooper <andrew.cooper3@...rix.com>
Cc: linux-kernel@...r.kernel.org, seanjc@...gle.com, pbonzini@...hat.com,
        tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
        dave.hansen@...ux.intel.com, x86@...nel.org, hpa@...or.com,
        kvm@...r.kernel.org, thomas.lendacky@....com, pgonda@...gle.com,
        sidtelang@...gle.com, mizhang@...gle.com,
        virtualization@...ts.linux.dev, xen-devel@...ts.xenproject.org,
        bcm-kernel-feedback-list@...adcom.com
Subject: Re: [RFC PATCH 1/2] x86, lib, xenpv: Add WBNOINVD helper functions

On 12/2/2024 5:44 PM, Kevin Loughlin wrote:
> On Mon, Dec 2, 2024 at 5:28 PM Andrew Cooper <andrew.cooper3@...rix.com> wrote:
>>
>> On 03/12/2024 12:59 am, Kevin Loughlin wrote:
>>> diff --git a/arch/x86/include/asm/paravirt.h b/arch/x86/include/asm/paravirt.h
>>> index d4eb9e1d61b8..c040af2d8eff 100644
>>> --- a/arch/x86/include/asm/paravirt.h
>>> +++ b/arch/x86/include/asm/paravirt.h
>>> @@ -187,6 +187,13 @@ static __always_inline void wbinvd(void)
>>>        PVOP_ALT_VCALL0(cpu.wbinvd, "wbinvd", ALT_NOT_XEN);
>>>   }
>>>
>>> +extern noinstr void pv_native_wbnoinvd(void);
>>> +
>>> +static __always_inline void wbnoinvd(void)
>>> +{
>>> +     PVOP_ALT_VCALL0(cpu.wbnoinvd, "wbnoinvd", ALT_NOT_XEN);
>>> +}
>>
>> Given this, ...
>>
>>> diff --git a/arch/x86/kernel/paravirt.c b/arch/x86/kernel/paravirt.c
>>> index fec381533555..a66b708d8a1e 100644
>>> --- a/arch/x86/kernel/paravirt.c
>>> +++ b/arch/x86/kernel/paravirt.c
>>> @@ -149,6 +154,7 @@ struct paravirt_patch_template pv_ops = {
>>>        .cpu.write_cr0          = native_write_cr0,
>>>        .cpu.write_cr4          = native_write_cr4,
>>>        .cpu.wbinvd             = pv_native_wbinvd,
>>> +     .cpu.wbnoinvd           = pv_native_wbnoinvd,
>>>        .cpu.read_msr           = native_read_msr,
>>>        .cpu.write_msr          = native_write_msr,
>>>        .cpu.read_msr_safe      = native_read_msr_safe,
>>
>> this, and ...
>>
>>> diff --git a/arch/x86/xen/enlighten_pv.c b/arch/x86/xen/enlighten_pv.c
>>> index d6818c6cafda..a5c76a6f8976 100644
>>> --- a/arch/x86/xen/enlighten_pv.c
>>> +++ b/arch/x86/xen/enlighten_pv.c
>>> @@ -1162,6 +1162,7 @@ static const typeof(pv_ops) xen_cpu_ops __initconst = {
>>>                .write_cr4 = xen_write_cr4,
>>>
>>>                .wbinvd = pv_native_wbinvd,
>>> +             .wbnoinvd = pv_native_wbnoinvd,
>>>
>>>                .read_msr = xen_read_msr,
>>>                .write_msr = xen_write_msr,
>>
>> this, what is the point having a paravirt hook which is wired to
>> native_wbnoinvd() in all cases?
>>
>> That just seems like overhead for overhead sake.
> 
> I'm mirroring what's done for WBINVD here, which was changed to a
> paravirt hook in 10a099405fdf ("cpuidle, xenpv: Make more PARAVIRT_XXL
> noinstr clean") in order to avoid calls out to instrumented code as
> described in the commit message in more detail. I believe a hook is
> similarly required for WBNOINVD, but please let me know if you
> disagree. Thanks!

Then the question is why we need to add WBINVD/WBNOINVD to the paravirt
hooks.