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

[Juergen Gross <jgross@xxxxxxxx>]

On 06.10.22 18:04, Oleksandr Tyshchenko wrote:
> 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@xxxxxxxx>
> > ---
> >    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).
Yes.

> > +
> > +       if (ret)
> > +               xen_grant_setup_dma_ops(dev->dev.parent);
> > +
> > +       return ret;
> > +}
> > +
> >    MODULE_DESCRIPTION("Xen grant DMA-mapping layer");
> >    MODULE_AUTHOR("Juergen Gross <jgross@xxxxxxxx>");
> >    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.
Indeed.


Juergen

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