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SubjectRe: [v3 1/1] x86/cpufeatures: Implement Predictive Store Forwarding control.
> +       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.
---
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 ?)


Thanks,
Reiji

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