Re: [Xen-devel] [PATCH v3 1/2] x86: add p2m_mmio_write_dm

[Paul Durrant <Paul.Durrant@xxxxxxxxxx>]

> -----Original Message-----
> From: Wei Ye [mailto:wei.ye@xxxxxxxxx]
> Sent: 03 September 2014 22:53
> To: xen-devel@xxxxxxxxxxxxx
> Cc: JBeulich@xxxxxxxx; Ian Campbell; Paul Durrant; Ian Jackson; Stefano
> Stabellini; donald.d.dugger@xxxxxxxxx; Kevin Tian; yang.z.zhang@xxxxxxxxx;
> zhiyuan.lv@xxxxxxxxx; konrad.wilk@xxxxxxxxxx; Keir (Xen.org); Tim
> (Xen.org); Wei Ye
> Subject: [PATCH v3 1/2] x86: add p2m_mmio_write_dm
> 
> Add an new p2m type p2m_mmio_write_dm. Page of this type is read
> only, and write will go to the device model for emulation just like
> a mmio.
> 

I realise this is a bit beyond the scope of this what you're doing but it 
occurs to me that the idea of p2m_mmio_read_dm might be equally useful when 
emulating MMIO that has read side effects but no write side effects. May save a 
few VMEXITs here and there.

> Signed-off-by: Wei Ye <wei.ye@xxxxxxxxx>
> ---
>  xen/arch/x86/hvm/hvm.c    |    3 ++-
>  xen/arch/x86/mm/p2m-ept.c |    1 +
>  xen/arch/x86/mm/p2m-pt.c  |    1 +
>  xen/include/asm-x86/p2m.h |    1 +
>  4 files changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
> index 17ff011..adc0f93 100644
> --- a/xen/arch/x86/hvm/hvm.c
> +++ b/xen/arch/x86/hvm/hvm.c
> @@ -2739,7 +2739,8 @@ int hvm_hap_nested_page_fault(paddr_t gpa,
>       * to the mmio handler.
>       */
>      if ( (p2mt == p2m_mmio_dm) ||
> -         (access_w && (p2mt == p2m_ram_ro)) )
> +         (access_w && ((p2mt == p2m_ram_ro) ||
> +         (p2mt == p2m_mmio_write_dm))) )

Personally I would have put the two p2m_mmio checks next to each other, but it 
doesn't really matter.

  Paul

>      {
>          put_gfn(p2m->domain, gfn);
> 
> diff --git a/xen/arch/x86/mm/p2m-ept.c b/xen/arch/x86/mm/p2m-ept.c
> index 15c6e83..e21a92d 100644
> --- a/xen/arch/x86/mm/p2m-ept.c
> +++ b/xen/arch/x86/mm/p2m-ept.c
> @@ -136,6 +136,7 @@ static void ept_p2m_type_to_flags(ept_entry_t
> *entry, p2m_type_t type, p2m_acces
>              entry->x = 0;
>              break;
>          case p2m_grant_map_ro:
> +        case p2m_mmio_write_dm:
>              entry->r = 1;
>              entry->w = entry->x = 0;
>              break;
> diff --git a/xen/arch/x86/mm/p2m-pt.c b/xen/arch/x86/mm/p2m-pt.c
> index 085ab6f..6a18606 100644
> --- a/xen/arch/x86/mm/p2m-pt.c
> +++ b/xen/arch/x86/mm/p2m-pt.c
> @@ -94,6 +94,7 @@ static unsigned long p2m_type_to_flags(p2m_type_t t,
> mfn_t mfn)
>      default:
>          return flags | _PAGE_NX_BIT;
>      case p2m_grant_map_ro:
> +    case p2m_mmio_write_dm:
>          return flags | P2M_BASE_FLAGS | _PAGE_NX_BIT;
>      case p2m_ram_ro:
>      case p2m_ram_logdirty:
> diff --git a/xen/include/asm-x86/p2m.h b/xen/include/asm-x86/p2m.h
> index 0ddbadb..523c7a9 100644
> --- a/xen/include/asm-x86/p2m.h
> +++ b/xen/include/asm-x86/p2m.h
> @@ -71,6 +71,7 @@ typedef enum {
>      p2m_ram_shared = 12,          /* Shared or sharable memory */
>      p2m_ram_broken = 13,          /* Broken page, access cause domain crash 
> */
>      p2m_map_foreign  = 14,        /* ram pages from foreign domain */
> +    p2m_mmio_write_dm = 15,       /* Read-only; write go to the device
> model */
>  } p2m_type_t;
> 
>  /*
> --
> 1.7.9.5


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