Re: [PATCH v2 33/35] x86/domain: implement domain_has_vuart()

["Roger Pau Monné" <roger.pau@citrix.com>]

On Thu, Dec 05, 2024 at 08:42:03PM -0800, Denis Mukhin via B4 Relay wrote:
> From: Denis Mukhin <dmukhin@ford.com>
> 
> Add new emulation flag for virtual UART on x86 and plumb it through the stack.
> 
> This change enables NS8250 emulator initialization.
> 
> Signed-off-by: Denis Mukhin <dmukhin@ford.com>
> ---
>  tools/libs/light/libxl_x86.c      |  6 +++++-
>  tools/ocaml/libs/xc/xenctrl.ml    |  1 +
>  tools/ocaml/libs/xc/xenctrl.mli   |  1 +
>  tools/python/xen/lowlevel/xc/xc.c |  4 +---
>  xen/arch/x86/domain.c             |  8 +++++---
>  xen/arch/x86/include/asm/domain.h |  7 ++++---
>  xen/include/public/arch-x86/xen.h | 14 +++++++++++++-
>  7 files changed, 30 insertions(+), 11 deletions(-)
> 
> diff --git a/tools/libs/light/libxl_x86.c b/tools/libs/light/libxl_x86.c
> index a3164a3077fec7e1b81a34074894dc646954a49a..de5f05e18cb0671bb031b101b9a7159eb0fe0178 100644
> --- a/tools/libs/light/libxl_x86.c
> +++ b/tools/libs/light/libxl_x86.c
> @@ -8,7 +8,11 @@ int libxl__arch_domain_prepare_config(libxl__gc *gc,
>  {
>      switch(d_config->c_info.type) {
>      case LIBXL_DOMAIN_TYPE_HVM:
> -        config->arch.emulation_flags = (XEN_X86_EMU_ALL & ~XEN_X86_EMU_VPCI);
> +        config->arch.emulation_flags = XEN_X86_EMU_ALL;
> +        config->arch.emulation_flags &= ~XEN_X86_EMU_VPCI;
> +        /* Virtual UART is selected at Xen build time */
> +        config->arch.emulation_flags &= ~XEN_X86_EMU_VUART;
> +
>          if (!libxl_defbool_val(d_config->b_info.u.hvm.pirq))
>              config->arch.emulation_flags &= ~XEN_X86_EMU_USE_PIRQ;
>          break;
> diff --git a/tools/ocaml/libs/xc/xenctrl.ml b/tools/ocaml/libs/xc/xenctrl.ml
> index 2690f9a92316b812ad3d3ff0e1c36823070adb4a..647239b3e55e88b00eb8e9773a5267894cbbae54 100644
> --- a/tools/ocaml/libs/xc/xenctrl.ml
> +++ b/tools/ocaml/libs/xc/xenctrl.ml
> @@ -47,6 +47,7 @@ type x86_arch_emulation_flags =
>    | X86_EMU_PIT
>    | X86_EMU_USE_PIRQ
>    | X86_EMU_VPCI
> +  | X86_EMU_VUART
>  
>  type x86_arch_misc_flags =
>    | X86_MSR_RELAXED
> diff --git a/tools/ocaml/libs/xc/xenctrl.mli b/tools/ocaml/libs/xc/xenctrl.mli
> index febbe1f6ae3f10c5abe45eaa3c06a8a67d9ba268..4f5f64c786e83e8a0c3dd3cdb0460f7095de4a62 100644
> --- a/tools/ocaml/libs/xc/xenctrl.mli
> +++ b/tools/ocaml/libs/xc/xenctrl.mli
> @@ -41,6 +41,7 @@ type x86_arch_emulation_flags =
>    | X86_EMU_PIT
>    | X86_EMU_USE_PIRQ
>    | X86_EMU_VPCI
> +  | X86_EMU_VUART
>  
>  type x86_arch_misc_flags =
>    | X86_MSR_RELAXED
> diff --git a/tools/python/xen/lowlevel/xc/xc.c b/tools/python/xen/lowlevel/xc/xc.c
> index 9feb12ae2b16e48cb5d0c3c45044ae226f152f2d..e54308956efc7061d58d2166ec9a95bc1dcd1781 100644
> --- a/tools/python/xen/lowlevel/xc/xc.c
> +++ b/tools/python/xen/lowlevel/xc/xc.c
> @@ -159,9 +159,7 @@ static PyObject *pyxc_domain_create(XcObject *self,
>  
>  #if defined (__i386) || defined(__x86_64__)
>      if ( config.flags & XEN_DOMCTL_CDF_hvm )
> -        config.arch.emulation_flags = XEN_X86_EMU_ALL &
> -                                      ~(XEN_X86_EMU_VPCI |
> -                                        XEN_X86_EMU_USE_PIRQ);
> +        config.arch.emulation_flags = XEN_X86_EMU_HVM_ALLOWABLE;
>  #elif defined (__arm__) || defined(__aarch64__)
>      config.arch.gic_version = XEN_DOMCTL_CONFIG_GIC_NATIVE;
>  #else
> diff --git a/xen/arch/x86/domain.c b/xen/arch/x86/domain.c
> index c88d422a64544531c1e1058fa484364bb4277d1e..439da7adc92a3a8eb481075bf834da5f9670dd54 100644
> --- a/xen/arch/x86/domain.c
> +++ b/xen/arch/x86/domain.c
> @@ -752,10 +752,10 @@ static bool emulation_flags_ok(const struct domain *d, uint32_t emflags)
>          if ( is_hardware_domain(d) &&
>               emflags != (X86_EMU_VPCI | X86_EMU_LAPIC | X86_EMU_IOAPIC) )
>              return false;
> +
> +        emflags &= ~X86_EMU_VUART;

I think you want to allow X86_EMU_VUART only for domains created by
Xen itself, so X86_EMU_VUART can only be valid if system_state <
SYS_STATE_active.

>          if ( !is_hardware_domain(d) &&
> -             /* HVM PIRQ feature is user-selectable. */
> -             (emflags & ~X86_EMU_USE_PIRQ) !=
> -             (X86_EMU_ALL & ~(X86_EMU_VPCI | X86_EMU_USE_PIRQ)) &&
> +             xen_emflags_allowable(emflags) != XEN_X86_EMU_HVM_ALLOWABLE &&
>               emflags != X86_EMU_LAPIC )
>              return false;
>      }
> @@ -806,6 +806,8 @@ int arch_domain_create(struct domain *d,
>  
>      emflags = config->arch.emulation_flags;
>  
> +    if ( IS_ENABLED(CONFIG_HAS_VUART_NS8250) && is_hvm_domain(d) )
> +        emflags |= XEN_X86_EMU_VUART;

Doesn't this need to be limited to domains created by Xen itself, as
otherwise it's the toolstack that should specify the XEN_X86_EMU_VUART
flag, and even then the recommendation would be to use the vUART from
QEMU?

>      if ( is_hardware_domain(d) && is_pv_domain(d) )
>          emflags |= XEN_X86_EMU_PIT;
>  
> diff --git a/xen/arch/x86/include/asm/domain.h b/xen/arch/x86/include/asm/domain.h
> index c1d0d1f47324e8cc678a4c76c43f86820a89e7b3..dacea6e1aad46e9f8710b2202bb81203c5e92807 100644
> --- a/xen/arch/x86/include/asm/domain.h
> +++ b/xen/arch/x86/include/asm/domain.h
> @@ -484,7 +484,8 @@ struct arch_domain
>  #define X86_EMU_VPCI     0
>  #endif
>  
> -#define X86_EMU_PIT     XEN_X86_EMU_PIT
> +#define X86_EMU_PIT      XEN_X86_EMU_PIT

Unintended indentation change?

> +#define X86_EMU_VUART    XEN_X86_EMU_VUART
>  
>  /* This must match XEN_X86_EMU_ALL in xen.h */
>  #define X86_EMU_ALL             (X86_EMU_LAPIC | X86_EMU_HPET |         \
> @@ -492,7 +493,7 @@ struct arch_domain
>                                   X86_EMU_IOAPIC | X86_EMU_PIC |         \
>                                   X86_EMU_VGA | X86_EMU_IOMMU |          \
>                                   X86_EMU_PIT | X86_EMU_USE_PIRQ |       \
> -                                 X86_EMU_VPCI)
> +                                 X86_EMU_VPCI | X86_EMU_VUART)
>  
>  #define has_vlapic(d)      (!!((d)->arch.emulation_flags & X86_EMU_LAPIC))
>  #define has_vhpet(d)       (!!((d)->arch.emulation_flags & X86_EMU_HPET))
> @@ -507,7 +508,7 @@ struct arch_domain
>  #define has_vpci(d)        (!!((d)->arch.emulation_flags & X86_EMU_VPCI))
>  
>  /* NB: same symbol as in Arm port */
> -#define domain_has_vuart(d) false
> +#define domain_has_vuart(d) (!!((d)->arch.emulation_flags & X86_EMU_VUART))
>  
>  #define gdt_ldt_pt_idx(v) \
>        ((v)->vcpu_id >> (PAGETABLE_ORDER - GDT_LDT_VCPU_SHIFT))
> diff --git a/xen/include/public/arch-x86/xen.h b/xen/include/public/arch-x86/xen.h
> index fc2487986642a7694578ab9d2f5f16d09761bff8..e7922e3f9ddc1742a464d228807279839df31e52 100644
> --- a/xen/include/public/arch-x86/xen.h
> +++ b/xen/include/public/arch-x86/xen.h
> @@ -283,13 +283,25 @@ struct xen_arch_domainconfig {
>  #define XEN_X86_EMU_USE_PIRQ        (1U<<_XEN_X86_EMU_USE_PIRQ)
>  #define _XEN_X86_EMU_VPCI           10
>  #define XEN_X86_EMU_VPCI            (1U<<_XEN_X86_EMU_VPCI)
> +#define _XEN_X86_EMU_VUART          11
> +#define XEN_X86_EMU_VUART           (1U<<_XEN_X86_EMU_VUART)
>  
>  #define XEN_X86_EMU_ALL             (XEN_X86_EMU_LAPIC | XEN_X86_EMU_HPET |  \
>                                       XEN_X86_EMU_PM | XEN_X86_EMU_RTC |      \
>                                       XEN_X86_EMU_IOAPIC | XEN_X86_EMU_PIC |  \
>                                       XEN_X86_EMU_VGA | XEN_X86_EMU_IOMMU |   \
>                                       XEN_X86_EMU_PIT | XEN_X86_EMU_USE_PIRQ |\
> -                                     XEN_X86_EMU_VPCI)
> +                                     XEN_X86_EMU_VPCI | XEN_X86_EMU_VUART)
> +
> +/* HVM PIRQ feature is user-selectable (libxl). */
> +#define XEN_X86_EMU_HVM_SELECTABLE  (XEN_X86_EMU_VPCI | \
> +                                     XEN_X86_EMU_USE_PIRQ | \
> +                                     XEN_X86_EMU_VUART)

XEN_X86_EMU_HVM_OPTIONAL is maybe clearer?

Albeit PVH is kind of HVM.

> +
> +#define xen_emflags_allowable(x)    ((x) & ~XEN_X86_EMU_HVM_SELECTABLE)
> +
> +#define XEN_X86_EMU_HVM_ALLOWABLE   xen_emflags_allowable(XEN_X86_EMU_ALL)

XEN_X86_EMU_HVM_BASELINE I think would also be better?

Thanks, Roger.