linux-kernel - Re: [PATCH 3/3] xen/virtio: enable grant based virtio on x86

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Date:   Thu, 6 Oct 2022 16:04:21 +0000
From:   Oleksandr Tyshchenko <Oleksandr_Tyshchenko@...m.com>
To:     Juergen Gross <jgross@...e.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "x86@...nel.org" <x86@...nel.org>
CC:     Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Stefano Stabellini <sstabellini@...nel.org>,
        "xen-devel@...ts.xenproject.org" <xen-devel@...ts.xenproject.org>
Subject: Re: [PATCH 3/3] xen/virtio: enable grant based virtio on x86


On 06.10.22 10:15, Juergen Gross wrote:


Hello Juergen

> Use an x86-specific virtio_check_mem_acc_cb() for Xen in order to setup
> the correct DMA ops.
>
> Signed-off-by: Juergen Gross <jgross@...e.com>
> ---
>   arch/x86/xen/enlighten_hvm.c |  2 +-
>   arch/x86/xen/enlighten_pv.c  |  2 +-
>   drivers/xen/grant-dma-ops.c  | 10 ++++++++++
>   include/xen/xen-ops.h        |  1 +
>   4 files changed, 13 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/xen/enlighten_hvm.c b/arch/x86/xen/enlighten_hvm.c
> index 1c1ac418484b..c1cd28e915a3 100644
> --- a/arch/x86/xen/enlighten_hvm.c
> +++ b/arch/x86/xen/enlighten_hvm.c
> @@ -212,7 +212,7 @@ static void __init xen_hvm_guest_init(void)
>   		return;
>   
>   	if (IS_ENABLED(CONFIG_XEN_VIRTIO_FORCE_GRANT))
> -		virtio_set_mem_acc_cb(virtio_require_restricted_mem_acc);
> +		virtio_set_mem_acc_cb(xen_virtio_restricted_mem_acc);
>   
>   	init_hvm_pv_info();
>   
> diff --git a/arch/x86/xen/enlighten_pv.c b/arch/x86/xen/enlighten_pv.c
> index 9b1a58dda935..45b24c1b646a 100644
> --- a/arch/x86/xen/enlighten_pv.c
> +++ b/arch/x86/xen/enlighten_pv.c
> @@ -112,7 +112,7 @@ static void __init xen_pv_init_platform(void)
>   {
>   	/* PV guests can't operate virtio devices without grants. */
>   	if (IS_ENABLED(CONFIG_XEN_VIRTIO))
> -		virtio_set_mem_acc_cb(virtio_require_restricted_mem_acc);
> +		virtio_set_mem_acc_cb(xen_virtio_restricted_mem_acc);
>   
>   	populate_extra_pte(fix_to_virt(FIX_PARAVIRT_BOOTMAP));
>   
> diff --git a/drivers/xen/grant-dma-ops.c b/drivers/xen/grant-dma-ops.c
> index a00112235877..60a7acc334ed 100644
> --- a/drivers/xen/grant-dma-ops.c
> +++ b/drivers/xen/grant-dma-ops.c
> @@ -372,6 +372,16 @@ void xen_grant_setup_dma_ops(struct device *dev)
>   	dev_err(dev, "Cannot set up Xen grant DMA ops, retain platform DMA ops\n");
>   }
>   
> +bool xen_virtio_restricted_mem_acc(struct virtio_device *dev)
> +{
> +	bool ret = xen_virtio_mem_acc(dev);


The grant usage is mandatory for PV guests, right?

Then xen_virtio_mem_acc() should always return true for PV guests (I 
mean even if CONFIG_XEN_VIRTIO_FORCE_GRANT is not set).



> +
> +	if (ret)
> +		xen_grant_setup_dma_ops(dev->dev.parent);
> +
> +	return ret;
> +}
> +
>   MODULE_DESCRIPTION("Xen grant DMA-mapping layer");
>   MODULE_AUTHOR("Juergen Gross <jgross@...e.com>");
>   MODULE_LICENSE("GPL");
> diff --git a/include/xen/xen-ops.h b/include/xen/xen-ops.h
> index dae0f350c678..3dd5aa936f1d 100644
> --- a/include/xen/xen-ops.h
> +++ b/include/xen/xen-ops.h
> @@ -219,6 +219,7 @@ static inline void xen_preemptible_hcall_end(void) { }
>   void xen_grant_setup_dma_ops(struct device *dev);
>   bool xen_is_grant_dma_device(struct device *dev);
>   bool xen_virtio_mem_acc(struct virtio_device *dev);
> +bool xen_virtio_restricted_mem_acc(struct virtio_device *dev);
>   #else
>   static inline void xen_grant_setup_dma_ops(struct device *dev)
>   {


And probably static inline stub always returning false if 
CONFIG_XEN_GRANT_DMA_OPS is not set.


-- 
Regards,

Oleksandr Tyshchenko