[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [Xen-devel] [PATCH v2] x86: suppress XPTI-related TLB flushes when possible
When there's no XPTI-enabled PV domain at all, there's no need to issue respective TLB flushes. Hardwire opt_xpti_* to false when !PV, and record the creation of PV domains by bumping opt_xpti_* accordingly. As to the sticky opt_xpti_domu vs increment/decrement of opt_xpti_hwdom, this is done this way to avoid (a) widening the former variable, (b) any risk of a missed flush, which would result in an XSA if a DomU was able to exercise it, and (c) any races updating the variable. Fundamentally the TLB flush done when context switching out the domain's vCPU-s the last time before destroying the domain ought to be sufficient, so in principle DomU handling could be made match hwdom's. Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx> --- v2: Add comment to spec_ctrl.h. Explain difference in accounting of DomU and hwdom. --- TBD: The hardwiring to false could be extended to opt_pv_l1tf_* and (for !HVM) opt_l1d_flush as well. --- a/xen/arch/x86/flushtlb.c +++ b/xen/arch/x86/flushtlb.c @@ -218,7 +218,7 @@ unsigned int flush_area_local(const void */ invpcid_flush_one(PCID_PV_PRIV, addr); invpcid_flush_one(PCID_PV_USER, addr); - if ( opt_xpti_hwdom || opt_xpti_domu ) + if ( opt_xpti_hwdom > 1 || opt_xpti_domu > 1 ) { invpcid_flush_one(PCID_PV_PRIV | PCID_PV_XPTI, addr); invpcid_flush_one(PCID_PV_USER | PCID_PV_XPTI, addr); --- a/xen/arch/x86/pv/domain.c +++ b/xen/arch/x86/pv/domain.c @@ -272,6 +272,9 @@ void pv_domain_destroy(struct domain *d) destroy_perdomain_mapping(d, GDT_LDT_VIRT_START, GDT_LDT_MBYTES << (20 - PAGE_SHIFT)); + opt_xpti_hwdom -= IS_ENABLED(CONFIG_LATE_HWDOM) && + !d->domain_id && opt_xpti_hwdom; + XFREE(d->arch.pv.cpuidmasks); FREE_XENHEAP_PAGE(d->arch.pv.gdt_ldt_l1tab); @@ -310,7 +313,16 @@ int pv_domain_initialise(struct domain * /* 64-bit PV guest by default. */ d->arch.is_32bit_pv = d->arch.has_32bit_shinfo = 0; - d->arch.pv.xpti = is_hardware_domain(d) ? opt_xpti_hwdom : opt_xpti_domu; + if ( is_hardware_domain(d) && opt_xpti_hwdom ) + { + d->arch.pv.xpti = true; + ++opt_xpti_hwdom; + } + if ( !is_hardware_domain(d) && opt_xpti_domu ) + { + d->arch.pv.xpti = true; + opt_xpti_domu = 2; + } if ( !is_pv_32bit_domain(d) && use_invpcid && cpu_has_pcid ) switch ( ACCESS_ONCE(opt_pcid) ) --- a/xen/arch/x86/spec_ctrl.c +++ b/xen/arch/x86/spec_ctrl.c @@ -80,10 +80,12 @@ static int __init parse_spec_ctrl(const opt_eager_fpu = 0; +#ifdef CONFIG_PV if ( opt_xpti_hwdom < 0 ) opt_xpti_hwdom = 0; if ( opt_xpti_domu < 0 ) opt_xpti_domu = 0; +#endif if ( opt_smt < 0 ) opt_smt = 1; @@ -634,6 +636,7 @@ static __init void l1tf_calculations(uin : (3ul << (paddr_bits - 2)))); } +#ifdef CONFIG_PV int8_t __read_mostly opt_xpti_hwdom = -1; int8_t __read_mostly opt_xpti_domu = -1; @@ -700,6 +703,9 @@ static __init int parse_xpti(const char return rc; } custom_param("xpti", parse_xpti); +#else /* !CONFIG_PV */ +# define xpti_init_default(caps) ((void)(caps)) +#endif /* CONFIG_PV */ void __init init_speculation_mitigations(void) { --- a/xen/include/asm-x86/spec_ctrl.h +++ b/xen/include/asm-x86/spec_ctrl.h @@ -43,7 +43,18 @@ extern bool bsp_delay_spec_ctrl; extern uint8_t default_xen_spec_ctrl; extern uint8_t default_spec_ctrl_flags; +#ifdef CONFIG_PV +/* + * Values -1, 0, and 1 have the usual meaning of "not established yet", + * "disabled", and "enabled". Values larger than 1 indicate there's actually + * at least one such domain (or there has been). This way XPTI-specific TLB + * flushes can be avoided when no XPTI-enabled domain is/was active. + */ extern int8_t opt_xpti_hwdom, opt_xpti_domu; +#else +# define opt_xpti_hwdom false +# define opt_xpti_domu false +#endif extern int8_t opt_pv_l1tf_hwdom, opt_pv_l1tf_domu; _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxxx https://lists.xenproject.org/mailman/listinfo/xen-devel
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