Re: [Xen-devel] [PATCH v2 06/12] xen/gnttab: Pass max_{grant, maptrack}_frames into grant_table_create()

[Julien Grall <julien.grall@xxxxxxx>]

Hi Andrew,

On 08/13/2018 11:01 AM, Andrew Cooper wrote:
> ... rather than setting the limits up after domain_create() has completed.
>
> This removes all the gnttab infrastructure for calculating the number of dom0
> grant frames, opting instead to require the dom0 construction code to pass a
> sane value in via the configuration.
>
> In practice, this now means that there is never a partially constructed grant
> table for a reference-able domain.
>
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> ---
> CC: Jan Beulich <JBeulich@xxxxxxxx>
> CC: Stefano Stabellini <sstabellini@xxxxxxxxxx>
> CC: Julien Grall <julien.grall@xxxxxxx>
> CC: Wei Liu <wei.liu2@xxxxxxxxxx>
>
> v2:
>   * Split/rearrange to avoid the post-domain-create error path.
> ---
>   xen/arch/arm/domain_build.c       |  3 ++-
>   xen/arch/arm/setup.c              | 12 ++++++++++++
>   xen/arch/x86/setup.c              |  3 +++
>   xen/common/domain.c               |  3 ++-
>   xen/common/grant_table.c          | 16 +++-------------
>   xen/include/asm-arm/grant_table.h | 12 ------------
>   xen/include/asm-x86/grant_table.h |  5 -----
>   xen/include/xen/grant_table.h     |  6 ++----
>   8 files changed, 24 insertions(+), 36 deletions(-)
>
> diff --git a/xen/arch/arm/domain_build.c b/xen/arch/arm/domain_build.c
> index 1351572..737e0f3 100644
> --- a/xen/arch/arm/domain_build.c
> +++ b/xen/arch/arm/domain_build.c
> @@ -2079,7 +2079,8 @@ static void __init find_gnttab_region(struct domain *d,
>        * enough space for a large grant table
>        */
>       kinfo->gnttab_start = __pa(_stext);
> -    kinfo->gnttab_size = gnttab_dom0_frames() << PAGE_SHIFT;
> +    kinfo->gnttab_size = min_t(unsigned int, opt_max_grant_frames,
> +                               PFN_DOWN(_etext - _stext)) << PAGE_SHIFT;

I agree with Jan's comment on v1 that there is a risk someone will 
update the size here but ...

>   
>   #ifdef CONFIG_ARM_32
>       /*
> diff --git a/xen/arch/arm/setup.c b/xen/arch/arm/setup.c
> index 45f3841..3d3b30c 100644
> --- a/xen/arch/arm/setup.c
> +++ b/xen/arch/arm/setup.c
> @@ -20,6 +20,7 @@
>   #include <xen/compile.h>
>   #include <xen/device_tree.h>
>   #include <xen/domain_page.h>
> +#include <xen/grant_table.h>
>   #include <xen/types.h>
>   #include <xen/string.h>
>   #include <xen/serial.h>
> @@ -693,6 +694,17 @@ void __init start_xen(unsigned long boot_phys_offset,
>       struct domain *dom0;
>       struct xen_domctl_createdomain dom0_cfg = {
>           .max_evtchn_port = -1,
> +
> +        /*
> +         * The region used by Xen on the memory will never be mapped in DOM0
> +         * memory layout. Therefore it can be used for the grant table.
> +         *
> +         * Only use the text section as it's always present and will contain
> +         * enough space for a large grant table
> +         */
> +        .max_grant_frames = min_t(unsigned int, opt_max_grant_frames,
> +                                  PFN_DOWN(_etext - _stext)),
... not here. So I would prefer if we either keep an helper to find the 
size of pass that size around to domain_build. Do we store the size in 
the domain information?
Cheers,

--
Julien Grall

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