lkml.org 
[lkml]   [2021]   [Apr]   [29]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [v3 1/1] x86/cpufeatures: Implement Predictive Store Forwarding control.
From
Date


On 4/29/2021 12:38 AM, Reiji Watanabe wrote:
>> + if (!strcmp(str, "off")) {
>> + set_cpu_cap(&boot_cpu_data, X86_FEATURE_MSR_SPEC_CTRL);
>> + x86_spec_ctrl_base |= SPEC_CTRL_PSFD;
>> + wrmsrl(MSR_IA32_SPEC_CTRL, x86_spec_ctrl_base);
>
> My previous suggestion about updating MSR_IA32_SPEC_CTRL meant
> something like:
>
> rdmsrl(MSR_IA32_SPEC_CTRL, current);
> wrmsrl(MSR_IA32_SPEC_CTRL, current | SPEC_CTRL_PSFD);
>
> And this is to keep the behavior of code below check_bugs().
> (Or do you intentionally change it due to some reason ?)
> BTW, x86_spec_ctrl_base, which is updated in psf_cmdline(),
> would be overwritten by check_bugs() anyway as follows.
> ---

Since psf_cmdline() directly writes to the MSR itself (and it only does this)
if the feature is available (per CPUID), check_bugs() should be ok.

My patch for now does not depend on the value of x86_spec_ctrl_base after psf_cmdline()
finishes execution.

> void __init check_bugs(void)
> {
> <...>
> /*
> * Read the SPEC_CTRL MSR to account for reserved bits which may
> * have unknown values. AMD64_LS_CFG MSR is cached in the early AMD
> * init code as it is not enumerated and depends on the family.
> */
> if (boot_cpu_has(X86_FEATURE_MSR_SPEC_CTRL))
> rdmsrl(MSR_IA32_SPEC_CTRL, x86_spec_ctrl_base);
> <...>
> ---
>
>> + setup_clear_cpu_cap(X86_FEATURE_PSFD);
>
> Does X86_FEATURE_PSFD need to be cleared for the 'off' case ?
> Do you want to remove "psfd" from /proc/cpuinfo
> when PSFD is enabled ? (not when PSFD is disabled ?)
>
>
No, it should not be cleared, I agree.
But I did test with KVM (with my patch that is not here) and I do not see
issues (meaning user space guest in QEMU is seeing PSF CPUID guest capability)

I see no reason to clear this feature and I will submit a new patch with this and other changes.

> Thanks,
> Reiji
>

\
 
 \ /
  Last update: 2021-04-29 16:03    [W:0.084 / U:2.004 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site