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    SubjectRe: [PATCH v3 10/11] x86/mm: Enable CR4.PCIDE on supported systems
    On Tue, Jun 20, 2017 at 10:22:16PM -0700, Andy Lutomirski wrote:
    > We can use PCID if the CPU has PCID and PGE and we're not on Xen.
    >
    > By itself, this has no effect. The next patch will start using
    > PCID.
    >
    > Cc: Juergen Gross <jgross@suse.com>
    > Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
    > Signed-off-by: Andy Lutomirski <luto@kernel.org>
    > ---
    > arch/x86/include/asm/tlbflush.h | 8 ++++++++
    > arch/x86/kernel/cpu/common.c | 15 +++++++++++++++
    > arch/x86/xen/enlighten_pv.c | 6 ++++++
    > 3 files changed, 29 insertions(+)
    >
    > diff --git a/arch/x86/include/asm/tlbflush.h b/arch/x86/include/asm/tlbflush.h
    > index 87b13e51e867..57b305e13c4c 100644
    > --- a/arch/x86/include/asm/tlbflush.h
    > +++ b/arch/x86/include/asm/tlbflush.h
    > @@ -243,6 +243,14 @@ static inline void __flush_tlb_all(void)
    > __flush_tlb_global();
    > else
    > __flush_tlb();
    > +
    > + /*
    > + * Note: if we somehow had PCID but not PGE, then this wouldn't work --
    > + * we'd end up flushing kernel translations for the current ASID but
    > + * we might fail to flush kernel translations for other cached ASIDs.
    > + *
    > + * To avoid this issue, we force PCID off if PGE is off.
    > + */
    > }
    >
    > static inline void __flush_tlb_one(unsigned long addr)
    > diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
    > index 904485e7b230..01caf66b270f 100644
    > --- a/arch/x86/kernel/cpu/common.c
    > +++ b/arch/x86/kernel/cpu/common.c
    > @@ -1143,6 +1143,21 @@ static void identify_cpu(struct cpuinfo_x86 *c)
    > setup_smep(c);
    > setup_smap(c);
    >
    > + /* Set up PCID */
    > + if (cpu_has(c, X86_FEATURE_PCID)) {
    > + if (cpu_has(c, X86_FEATURE_PGE)) {

    What are we protecting ourselves here against? Funny virtualization guests?

    Because PGE should be ubiquitous by now. Or have you heard something?

    > + cr4_set_bits(X86_CR4_PCIDE);
    > + } else {
    > + /*
    > + * flush_tlb_all(), as currently implemented, won't
    > + * work if PCID is on but PGE is not. Since that
    > + * combination doesn't exist on real hardware, there's
    > + * no reason to try to fully support it.
    > + */
    > + clear_cpu_cap(c, X86_FEATURE_PCID);
    > + }
    > + }

    This whole in setup_pcid() I guess, like the rest of the features.

    > +
    > /*
    > * The vendor-specific functions might have changed features.
    > * Now we do "generic changes."
    > diff --git a/arch/x86/xen/enlighten_pv.c b/arch/x86/xen/enlighten_pv.c
    > index f33eef4ebd12..a136aac543c3 100644
    > --- a/arch/x86/xen/enlighten_pv.c
    > +++ b/arch/x86/xen/enlighten_pv.c
    > @@ -295,6 +295,12 @@ static void __init xen_init_capabilities(void)
    > setup_clear_cpu_cap(X86_FEATURE_ACC);
    > setup_clear_cpu_cap(X86_FEATURE_X2APIC);
    >
    > + /*
    > + * Xen PV would need some work to support PCID: CR3 handling as well
    > + * as xen_flush_tlb_others() would need updating.
    > + */
    > + setup_clear_cpu_cap(X86_FEATURE_PCID);
    > +
    > if (!xen_initial_domain())
    > setup_clear_cpu_cap(X86_FEATURE_ACPI);
    >
    > --
    > 2.9.4
    >

    --
    Regards/Gruss,
    Boris.

    Good mailing practices for 400: avoid top-posting and trim the reply.

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