Re: [Xen-devel] [PATCH v2 2/5] IOMMU: iommu_intpost is x86/HVM-only

["Tian, Kevin" <kevin.tian@xxxxxxxxx>]

> From: Jan Beulich <jbeulich@xxxxxxxx>
> Sent: Monday, March 9, 2020 6:43 PM
> 
> Provide a #define for all other cases.
> 
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
> ---
> v2: Refine doc adjustment.
> 
> --- a/docs/misc/xen-command-line.pandoc
> +++ b/docs/misc/xen-command-line.pandoc
> @@ -1309,6 +1309,8 @@ boolean (e.g. `iommu=no`) can override t
>      This option depends on `intremap`, and is disabled by default due to some
>      corner cases in the implementation which have yet to be resolved.
> 
> +    This option is only valid on x86, and only builds of Xen with HVM 
> support.
> +
>  *   The `crash-disable` boolean controls disabling IOMMU functionality
> (DMAR/IR/QI)
>      before switching to a crash kernel. This option is inactive by default 
> and
>      is for compatibility with older kdump kernels only. Modern kernels copy
> --- a/xen/drivers/passthrough/iommu.c
> +++ b/xen/drivers/passthrough/iommu.c
> @@ -43,14 +43,6 @@ bool __read_mostly iommu_hwdom_passthrou
>  bool __hwdom_initdata iommu_hwdom_inclusive;
>  int8_t __hwdom_initdata iommu_hwdom_reserved = -1;
> 
> -/*
> - * In the current implementation of VT-d posted interrupts, in some extreme
> - * cases, the per cpu list which saves the blocked vCPU will be very long,
> - * and this will affect the interrupt latency, so let this feature off by
> - * default until we find a good solution to resolve it.
> - */
> -bool_t __read_mostly iommu_intpost;
> -
>  #ifndef iommu_hap_pt_share
>  bool __read_mostly iommu_hap_pt_share = true;
>  #endif
> @@ -93,8 +85,10 @@ static int __init parse_iommu_param(cons
>          else if ( (val = parse_boolean("intremap", s, ss)) >= 0 )
>              iommu_intremap = val ? iommu_intremap_full : iommu_intremap_off;
>  #endif
> +#ifndef iommu_intpost
>          else if ( (val = parse_boolean("intpost", s, ss)) >= 0 )
>              iommu_intpost = val;
> +#endif
>  #ifdef CONFIG_KEXEC
>          else if ( (val = parse_boolean("crash-disable", s, ss)) >= 0 )
>              iommu_crash_disable = val;
> @@ -486,8 +480,10 @@ int __init iommu_setup(void)
>          panic("Couldn't enable %s and iommu=required/force\n",
>                !iommu_enabled ? "IOMMU" : "Interrupt Remapping");
> 
> +#ifndef iommu_intpost
>      if ( !iommu_intremap )
>          iommu_intpost = 0;
> +#endif
> 
>      printk("I/O virtualisation %sabled\n", iommu_enabled ? "en" : "dis");
>      if ( !iommu_enabled )
> @@ -563,10 +559,13 @@ void iommu_crash_shutdown(void)
> 
>      if ( iommu_enabled )
>          iommu_get_ops()->crash_shutdown();
> -    iommu_enabled = iommu_intpost = 0;
> +    iommu_enabled = false;
>  #ifndef iommu_intremap
>      iommu_intremap = iommu_intremap_off;
>  #endif
> +#ifndef iommu_intpost
> +    iommu_intpost = false;
> +#endif
>  }
> 
>  int iommu_get_reserved_device_memory(iommu_grdm_t *func, void *ctxt)
> --- a/xen/drivers/passthrough/vtd/iommu.c
> +++ b/xen/drivers/passthrough/vtd/iommu.c
> @@ -2297,13 +2297,15 @@ static int __init vtd_setup(void)
>          if ( iommu_intremap && !ecap_intr_remap(iommu->ecap) )
>              iommu_intremap = iommu_intremap_off;
> 
> +#ifndef iommu_intpost
>          /*
>           * We cannot use posted interrupt if X86_FEATURE_CX16 is
>           * not supported, since we count on this feature to
>           * atomically update 16-byte IRTE in posted format.
>           */
>          if ( !cap_intr_post(iommu->cap) || !iommu_intremap || !cpu_has_cx16 )
> -            iommu_intpost = 0;
> +            iommu_intpost = false;
> +#endif
> 
>          if ( !vtd_ept_page_compatible(iommu) )
>              clear_iommu_hap_pt_share();
> @@ -2330,7 +2332,9 @@ static int __init vtd_setup(void)
>      P(iommu_hwdom_passthrough, "Dom0 DMA Passthrough");
>      P(iommu_qinval, "Queued Invalidation");
>      P(iommu_intremap, "Interrupt Remapping");
> +#ifndef iommu_intpost
>      P(iommu_intpost, "Posted Interrupt");
> +#endif
>      P(iommu_hap_pt_share, "Shared EPT tables");
>  #undef P
> 
> @@ -2348,7 +2352,9 @@ static int __init vtd_setup(void)
>      iommu_hwdom_passthrough = false;
>      iommu_qinval = 0;
>      iommu_intremap = iommu_intremap_off;
> -    iommu_intpost = 0;
> +#ifndef iommu_intpost
> +    iommu_intpost = false;
> +#endif
>      return ret;
>  }
> 
> --- a/xen/drivers/passthrough/x86/iommu.c
> +++ b/xen/drivers/passthrough/x86/iommu.c
> @@ -29,6 +29,16 @@ struct iommu_ops __read_mostly iommu_ops
> 
>  enum iommu_intremap __read_mostly iommu_intremap =
> iommu_intremap_full;
> 
> +#ifndef iommu_intpost
> +/*
> + * In the current implementation of VT-d posted interrupts, in some
> extreme
> + * cases, the per cpu list which saves the blocked vCPU will be very long,
> + * and this will affect the interrupt latency, so let this feature off by
> + * default until we find a good solution to resolve it.
> + */

Is above comment really VT-d specific? may take this chance to refine
it together.

> +bool __read_mostly iommu_intpost;
> +#endif
> +
>  int __init iommu_hardware_setup(void)
>  {
>      struct IO_APIC_route_entry **ioapic_entries = NULL;
> --- a/xen/include/xen/iommu.h
> +++ b/xen/include/xen/iommu.h
> @@ -54,7 +54,7 @@ static inline bool_t dfn_eq(dfn_t x, dfn
> 
>  extern bool_t iommu_enable, iommu_enabled;
>  extern bool force_iommu, iommu_quarantine, iommu_verbose, iommu_igfx;
> -extern bool_t iommu_snoop, iommu_qinval, iommu_intpost;
> +extern bool_t iommu_snoop, iommu_qinval;
> 
>  #ifdef CONFIG_X86
>  extern enum __packed iommu_intremap {
> @@ -74,6 +74,12 @@ extern enum __packed iommu_intremap {
>  # define iommu_intremap false
>  #endif
> 
> +#if defined(CONFIG_X86) && defined(CONFIG_HVM)
> +extern bool iommu_intpost;
> +#else
> +# define iommu_intpost false
> +#endif
> +
>  #if defined(CONFIG_IOMMU_FORCE_PT_SHARE)
>  #define iommu_hap_pt_share true
>  #elif defined(CONFIG_HVM)

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