Re: [Xen-devel] [PATCH v2 2/3] x86/hyperv: skeleton for L0 assisted TLB flush

["Durrant, Paul" <pdurrant@xxxxxxxxxxxx>]

> -----Original Message-----
> From: Wei Liu <wei.liu.xen@xxxxxxxxx> On Behalf Of Wei Liu
> Sent: 14 February 2020 13:34
> To: Xen Development List <xen-devel@xxxxxxxxxxxxxxxxxxxx>
> Cc: Michael Kelley <mikelley@xxxxxxxxxxxxx>; Durrant, Paul
> <pdurrant@xxxxxxxxxxxx>; Wei Liu <liuwe@xxxxxxxxxxxxx>; Wei Liu
> <wl@xxxxxxx>; Jan Beulich <jbeulich@xxxxxxxx>; Andrew Cooper
> <andrew.cooper3@xxxxxxxxxx>; Roger Pau Monné <roger.pau@xxxxxxxxxx>
> Subject: [PATCH v2 2/3] x86/hyperv: skeleton for L0 assisted TLB flush
> 
> Implement a basic hook for L0 assisted TLB flush. The hook needs to
> check if prerequisites are met. If they are not met, it returns an error
> number to fall back to native flushes.
> 
> Introduce a new variable to indicate if hypercall page is ready.
> 
> Signed-off-by: Wei Liu <liuwe@xxxxxxxxxxxxx>
> ---
>  xen/arch/x86/guest/hyperv/Makefile  |  1 +
>  xen/arch/x86/guest/hyperv/hyperv.c  | 17 ++++++++++++
>  xen/arch/x86/guest/hyperv/private.h |  4 +++
>  xen/arch/x86/guest/hyperv/tlb.c     | 41 +++++++++++++++++++++++++++++
>  4 files changed, 63 insertions(+)
>  create mode 100644 xen/arch/x86/guest/hyperv/tlb.c
> 
> diff --git a/xen/arch/x86/guest/hyperv/Makefile
> b/xen/arch/x86/guest/hyperv/Makefile
> index 68170109a9..18902c33e9 100644
> --- a/xen/arch/x86/guest/hyperv/Makefile
> +++ b/xen/arch/x86/guest/hyperv/Makefile
> @@ -1 +1,2 @@
>  obj-y += hyperv.o
> +obj-y += tlb.o
> diff --git a/xen/arch/x86/guest/hyperv/hyperv.c
> b/xen/arch/x86/guest/hyperv/hyperv.c
> index 70f4cd5ae0..f9d1f11ae3 100644
> --- a/xen/arch/x86/guest/hyperv/hyperv.c
> +++ b/xen/arch/x86/guest/hyperv/hyperv.c
> @@ -33,6 +33,8 @@ DEFINE_PER_CPU_READ_MOSTLY(void *, hv_input_page);
>  DEFINE_PER_CPU_READ_MOSTLY(void *, hv_vp_assist);
>  DEFINE_PER_CPU_READ_MOSTLY(unsigned int, hv_vp_index);
> 
> +static bool __read_mostly hv_hcall_page_ready;
> +
>  static uint64_t generate_guest_id(void)
>  {
>      union hv_guest_os_id id = {};
> @@ -119,6 +121,8 @@ static void __init setup_hypercall_page(void)
>      BUG_ON(!hypercall_msr.enable);
> 
>      set_fixmap_x(FIX_X_HYPERV_HCALL, mfn << PAGE_SHIFT);

Shouldn't this have at least a compiler barrier here?

  Paul

> +
> +    hv_hcall_page_ready = true;
>  }
> 
>  static int setup_hypercall_pcpu_arg(void)
> @@ -199,11 +203,24 @@ static void __init e820_fixup(struct e820map *e820)
>          panic("Unable to reserve Hyper-V hypercall range\n");
>  }
> 
> +static int flush_tlb(const cpumask_t *mask, const void *va,
> +                     unsigned int flags)
> +{
> +    if ( !(ms_hyperv.hints & HV_X64_REMOTE_TLB_FLUSH_RECOMMENDED) )
> +        return -EOPNOTSUPP;
> +
> +    if ( !hv_hcall_page_ready || !this_cpu(hv_input_page) )
> +        return -ENXIO;
> +
> +    return hyperv_flush_tlb(mask, va, flags);
> +}
> +
>  static const struct hypervisor_ops __initdata ops = {
>      .name = "Hyper-V",
>      .setup = setup,
>      .ap_setup = ap_setup,
>      .e820_fixup = e820_fixup,
> +    .flush_tlb = flush_tlb,
>  };
> 
>  /*
> diff --git a/xen/arch/x86/guest/hyperv/private.h
> b/xen/arch/x86/guest/hyperv/private.h
> index 956eff831f..509bedaafa 100644
> --- a/xen/arch/x86/guest/hyperv/private.h
> +++ b/xen/arch/x86/guest/hyperv/private.h
> @@ -22,10 +22,14 @@
>  #ifndef __XEN_HYPERV_PRIVIATE_H__
>  #define __XEN_HYPERV_PRIVIATE_H__
> 
> +#include <xen/cpumask.h>
>  #include <xen/percpu.h>
> 
>  DECLARE_PER_CPU(void *, hv_input_page);
>  DECLARE_PER_CPU(void *, hv_vp_assist);
>  DECLARE_PER_CPU(unsigned int, hv_vp_index);
> 
> +int hyperv_flush_tlb(const cpumask_t *mask, const void *va,
> +                     unsigned int flags);
> +
>  #endif /* __XEN_HYPERV_PRIVIATE_H__  */
> diff --git a/xen/arch/x86/guest/hyperv/tlb.c
> b/xen/arch/x86/guest/hyperv/tlb.c
> new file mode 100644
> index 0000000000..48f527229e
> --- /dev/null
> +++ b/xen/arch/x86/guest/hyperv/tlb.c
> @@ -0,0 +1,41 @@
> +/************************************************************************
> ******
> + * arch/x86/guest/hyperv/tlb.c
> + *
> + * Support for TLB management using hypercalls
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License as published by
> + * the Free Software Foundation; either version 2 of the License, or
> + * (at your option) any later version.
> + *
> + * This program is distributed in the hope that it will be useful,
> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> + * GNU General Public License for more details.
> + *
> + * You should have received a copy of the GNU General Public License
> + * along with this program; If not, see <http://www.gnu.org/licenses/>.
> + *
> + * Copyright (c) 2020 Microsoft.
> + */
> +
> +#include <xen/cpumask.h>
> +#include <xen/errno.h>
> +
> +#include "private.h"
> +
> +int hyperv_flush_tlb(const cpumask_t *mask, const void *va,
> +                     unsigned int flags)
> +{
> +    return -EOPNOTSUPP;
> +}
> +
> +/*
> + * Local variables:
> + * mode: C
> + * c-file-style: "BSD"
> + * c-basic-offset: 4
> + * tab-width: 4
> + * indent-tabs-mode: nil
> + * End:
> + */
> --
> 2.20.1


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