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    SubjectRe: [PATCH RFC V2 04/17] x86/pks: Preserve the PKRS MSR on context switch
    On Fri, Jul 17, 2020 at 03:34:07PM -0700, Ira Weiny wrote:
    > On Fri, Jul 17, 2020 at 10:59:54AM +0200, Peter Zijlstra wrote:
    > > On Fri, Jul 17, 2020 at 12:20:43AM -0700, ira.weiny@intel.com wrote:
    > > > +/*
    > > > + * Write the PKey Register Supervisor. This must be run with preemption
    > > > + * disabled as it does not guarantee the atomicity of updating the pkrs_cache
    > > > + * and MSR on its own.
    > > > + */
    > > > +void write_pkrs(u32 pkrs_val)
    > > > +{
    > > > + this_cpu_write(pkrs_cache, pkrs_val);
    > > > + wrmsrl(MSR_IA32_PKRS, pkrs_val);
    > > > +}
    > >
    > > Should we write that like:
    > >
    > > void write_pkrs(u32 pkr)
    > > {
    > > u32 *pkrs = get_cpu_ptr(pkrs_cache);
    > > if (*pkrs != pkr) {
    > > *pkrs = pkr;
    > > wrmsrl(MSR_IA32_PKRS, pkr);
    > > }
    > > put_cpu_ptrpkrs_cache);
    > > }
    > >
    > > given that we fundamentally need to serialize againt schedule() here.
    >
    > Yes. That seems better.
    >
    > That also means pks_sched_in() can be simplified to just
    >
    > static inline void pks_sched_in(void)
    > {
    > write_pkrs(current->thread.saved_pkrs);
    > }
    >
    > Because of the built WRMSR avoidance.
    >
    > However, pkrs_cache is static so I think I need to use {get,put}_cpu_var() here
    > don't I?

    Or get_cpu_ptr(&pkrs_cache), sorry for the typo :-)

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