Re: [Xen-devel] [PATCH v3 1/6] domain: introduce alloc/free_shared_info() helpers...

["Xia, Hongyan" <hongyxia@amazon.com>]

On Thu, 2020-03-05 at 12:44 +0000, pdurrant@amzn.com wrote:
> From: Paul Durrant <pdurrant@amazon.com>
> 
> ... and save the MFN.
> 
> This patch modifies the 'shared_info' field of struct domain to be
> a structure comprising an MFN and a virtual address. Allocations are
> still done from xenheap, so the virtual address still equates to
> virt_to_mfn() called on the MFN but subsequent patch will change
> this.
> Hence the need to save the MFN.
> 
> NOTE: Whist defining the new helpers, virt_to_mfn() in
> common/domain.c
>       is made type safe.
>       The definition of nmi_reason() in asm-x86/shared.h is also re-
>       flowed to avoid overly long lines.
> 
> Signed-off-by: Paul Durrant <pdurrant@amazon.com>
> Reviewed-by: Julien Grall <julien@xen.org>
> ...
>  
> +int alloc_shared_info(struct domain *d, unsigned int memflags)
> +{
> +    if ( (d->shared_info.virt = alloc_xenheap_pages(0, memflags)) ==
> NULL )
> +        return -ENOMEM;
> +
> +    d->shared_info.mfn = virt_to_mfn(d->shared_info.virt);
> +
> +    clear_page(d->shared_info.virt);
> +    share_xen_page_with_guest(mfn_to_page(d->shared_info.mfn), d,
> SHARE_rw);
> +
> +    return 0;
> +}
> +
> +void free_shared_info(struct domain *d)
> +{
> +    if ( !d->shared_info.virt )
> +        return;
> +
> +    free_xenheap_page(d->shared_info.virt);
> +    d->shared_info.virt = NULL;
> +}
> +

I was going to say that free_xenheap_page() can deal with NULL so we do
not have to return on NULL. But then I found that the final patch needs
to unmap it which cannot deal with NULL anyway, so I no longer have a
strong opinion to do clean-ups here.

Other than that,
Reviewed-by: Hongyan Xia <hongyxia@amazon.org>

Hongyan
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