linux-kernel - Re: [PATCH v3] xen: share start flags between PV and PVH

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Date:   Fri, 8 Jun 2018 09:12:25 -0700 (PDT)
From:   Stefano Stabellini <sstabellini@...nel.org>
To:     Roger Pau Monne <roger.pau@...rix.com>
cc:     linux-kernel@...r.kernel.org,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Juergen Gross <jgross@...e.com>,
        Stefano Stabellini <sstabellini@...nel.org>,
        xen-devel@...ts.xenproject.org
Subject: Re: [PATCH v3] xen: share start flags between PV and PVH

On Fri, 8 Jun 2018, Roger Pau Monne wrote:
> Use a global variable to store the start flags for both PV and PVH.
> This allows the xen_initial_domain macro to work properly on PVH.
> 
> Note that ARM is also switched to use the new variable.
> 
> Signed-off-by: Boris Ostrovsky <boris.ostrovsky@...cle.com>
> Signed-off-by: Roger Pau Monné <roger.pau@...rix.com>

As I already mentioned, the ARM part is OK. However, is the issue that
xen_start_info is not available on PVH? We had the same problem on ARM
and solved it by faking a xen_start_info page, see the top of
arch/arm/xen/enlighten.c.

I would love to get rid of that, but to do that, we also need to remove
the xen_start_info referece at drivers/tty/hvc/hvc_xen.c:255:

  if (!xen_start_info->console.domU.evtchn)
		return -ENODEV;


> ---
> Cc: Boris Ostrovsky <boris.ostrovsky@...cle.com>
> Cc: Juergen Gross <jgross@...e.com>
> Cc: Stefano Stabellini <sstabellini@...nel.org>
> Cc: xen-devel@...ts.xenproject.org
> ---
> Changes since v2:
>  - Declare xen_start_flags outside of the XEN_DOM0 guard and include
>    types.h.
> 
> Changes since v1:
>  - Switch ARM to also use the new xen_start_flags.
> ---
>  arch/arm/xen/enlighten.c     | 7 ++++---
>  arch/x86/xen/enlighten.c     | 7 +++++++
>  arch/x86/xen/enlighten_pv.c  | 1 +
>  arch/x86/xen/enlighten_pvh.c | 1 +
>  include/xen/xen.h            | 6 +++++-
>  5 files changed, 18 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/arm/xen/enlighten.c b/arch/arm/xen/enlighten.c
> index ba7f4c8f5c3e..a99d5edf7bdf 100644
> --- a/arch/arm/xen/enlighten.c
> +++ b/arch/arm/xen/enlighten.c
> @@ -59,6 +59,9 @@ struct xen_memory_region xen_extra_mem[XEN_EXTRA_MEM_MAX_REGIONS] __initdata;
>  
>  static __read_mostly unsigned int xen_events_irq;
>  
> +uint32_t xen_start_flags;
> +EXPORT_SYMBOL(xen_start_flags);
> +
>  int xen_remap_domain_gfn_array(struct vm_area_struct *vma,
>  			       unsigned long addr,
>  			       xen_pfn_t *gfn, int nr,
> @@ -282,9 +285,7 @@ void __init xen_early_init(void)
>  	xen_setup_features();
>  
>  	if (xen_feature(XENFEAT_dom0))
> -		xen_start_info->flags |= SIF_INITDOMAIN|SIF_PRIVILEGED;
> -	else
> -		xen_start_info->flags &= ~(SIF_INITDOMAIN|SIF_PRIVILEGED);
> +		xen_start_flags |= SIF_INITDOMAIN|SIF_PRIVILEGED;
>  
>  	if (!console_set_on_cmdline && !xen_initial_domain())
>  		add_preferred_console("hvc", 0, NULL);
> diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
> index c9081c6671f0..3b5318505c69 100644
> --- a/arch/x86/xen/enlighten.c
> +++ b/arch/x86/xen/enlighten.c
> @@ -64,6 +64,13 @@ struct shared_info xen_dummy_shared_info;
>  __read_mostly int xen_have_vector_callback;
>  EXPORT_SYMBOL_GPL(xen_have_vector_callback);
>  
> +/*
> + * NB: needs to live in .data because it's used by xen_prepare_pvh which runs
> + * before clearing the bss.
> + */
> +uint32_t xen_start_flags __attribute__((section(".data"))) = 0;
> +EXPORT_SYMBOL(xen_start_flags);
> +
>  /*
>   * Point at some empty memory to start with. We map the real shared_info
>   * page as soon as fixmap is up and running.
> diff --git a/arch/x86/xen/enlighten_pv.c b/arch/x86/xen/enlighten_pv.c
> index 357969a3697c..8d4e2e1ae60b 100644
> --- a/arch/x86/xen/enlighten_pv.c
> +++ b/arch/x86/xen/enlighten_pv.c
> @@ -1203,6 +1203,7 @@ asmlinkage __visible void __init xen_start_kernel(void)
>  		return;
>  
>  	xen_domain_type = XEN_PV_DOMAIN;
> +	xen_start_flags = xen_start_info->flags;
>  
>  	xen_setup_features();
>  
> diff --git a/arch/x86/xen/enlighten_pvh.c b/arch/x86/xen/enlighten_pvh.c
> index aa1c6a6831a9..c85d1a88f476 100644
> --- a/arch/x86/xen/enlighten_pvh.c
> +++ b/arch/x86/xen/enlighten_pvh.c
> @@ -97,6 +97,7 @@ void __init xen_prepare_pvh(void)
>  	}
>  
>  	xen_pvh = 1;
> +	xen_start_flags = pvh_start_info.flags;
>  
>  	msr = cpuid_ebx(xen_cpuid_base() + 2);
>  	pfn = __pa(hypercall_page);
> diff --git a/include/xen/xen.h b/include/xen/xen.h
> index 9d4340c907d1..1e1d9bd0bd37 100644
> --- a/include/xen/xen.h
> +++ b/include/xen/xen.h
> @@ -25,12 +25,16 @@ extern bool xen_pvh;
>  #define xen_hvm_domain()	(xen_domain_type == XEN_HVM_DOMAIN)
>  #define xen_pvh_domain()	(xen_pvh)
>  
> +#include <linux/types.h>
> +
> +extern uint32_t xen_start_flags;
> +
>  #ifdef CONFIG_XEN_DOM0
>  #include <xen/interface/xen.h>
>  #include <asm/xen/hypervisor.h>
>  
>  #define xen_initial_domain()	(xen_domain() && \
> -				 xen_start_info && xen_start_info->flags & SIF_INITDOMAIN)
> +				 (xen_start_flags & SIF_INITDOMAIN))
>  #else  /* !CONFIG_XEN_DOM0 */
>  #define xen_initial_domain()	(0)
>  #endif	/* CONFIG_XEN_DOM0 */
> -- 
> 2.17.1
>