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SubjectRe: [PATCH v1] p2m: use GNTTABOP_unmap_and_duplicate if available
On Thu, 1 Aug 2013, Roger Pau Monne wrote:
> The new GNTTABOP_unmap_and_duplicate operation doesn't zero the
> mapping passed in new_addr, allowing us to perform batch unmaps in p2m
> code without requiring the use of a multicall.
>
> Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
> Cc: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
> Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
> Cc: David Vrabel <david.vrabel@citrix.com>

It looks pretty good overall.


> Changes since RFC:
> * Move shared code between _single and _batch to helper
> functions.
> ---
> I don't currently have a NFS server (the one I had is currently not
> working due to SD card corruption) and I cannot set up one right now,
> so I've only tested this with a raw image stored in a local disk.
> ---
> arch/x86/include/asm/xen/page.h | 4 +-
> arch/x86/xen/p2m.c | 154 +++++++++++++++++++++++++++++++----
> drivers/xen/grant-table.c | 24 ++----
> include/xen/interface/grant_table.h | 22 +++++
> 4 files changed, 169 insertions(+), 35 deletions(-)
>
> diff --git a/arch/x86/include/asm/xen/page.h b/arch/x86/include/asm/xen/page.h
> index 6aef9fb..ea1dce6 100644
> --- a/arch/x86/include/asm/xen/page.h
> +++ b/arch/x86/include/asm/xen/page.h
> @@ -51,8 +51,8 @@ extern unsigned long set_phys_range_identity(unsigned long pfn_s,
>
> extern int m2p_add_override(unsigned long mfn, struct page *page,
> struct gnttab_map_grant_ref *kmap_op);
> -extern int m2p_remove_override(struct page *page,
> - struct gnttab_map_grant_ref *kmap_op);
> +extern int m2p_remove_override(struct page **pages,
> + struct gnttab_map_grant_ref *kmap_ops, int count);
> extern struct page *m2p_find_override(unsigned long mfn);
> extern unsigned long m2p_find_override_pfn(unsigned long mfn, unsigned long pfn);
>
> diff --git a/arch/x86/xen/p2m.c b/arch/x86/xen/p2m.c
> index 0d4ec35..e92636c 100644
> --- a/arch/x86/xen/p2m.c
> +++ b/arch/x86/xen/p2m.c
> @@ -154,6 +154,8 @@
> #include <linux/hash.h>
> #include <linux/sched.h>
> #include <linux/seq_file.h>
> +#include <linux/slab.h>
> +#include <linux/hardirq.h>
>
> #include <asm/cache.h>
> #include <asm/setup.h>
> @@ -853,6 +855,7 @@ bool set_phys_to_machine(unsigned long pfn, unsigned long mfn)
>
> static RESERVE_BRK_ARRAY(struct list_head, m2p_overrides, M2P_OVERRIDE_HASH);
> static DEFINE_SPINLOCK(m2p_override_lock);
> +extern bool gnttab_supports_duplicate;

If you only use gnttab_supports_duplicate in the m2p, you might as well
make the variable static and initialize it from m2p_override_init.


> static void __init m2p_override_init(void)
> {
> @@ -933,8 +936,8 @@ int m2p_add_override(unsigned long mfn, struct page *page,
> return 0;
> }
> EXPORT_SYMBOL_GPL(m2p_add_override);
> -int m2p_remove_override(struct page *page,
> - struct gnttab_map_grant_ref *kmap_op)
> +
> +static inline int remove_page_override(struct page *page)
> {
> unsigned long flags;
> unsigned long mfn;
> @@ -965,6 +968,49 @@ int m2p_remove_override(struct page *page,
> ClearPagePrivate(page);
>
> set_phys_to_machine(pfn, page->index);
> +
> + return 0;
> +}
> +
> +static inline int check_duplicate_mfn(struct page *page, unsigned long mfn)
> +{
> + unsigned long pfn;
> + int ret = 0;
> +
> + /*
> + * p2m(m2p(mfn)) == FOREIGN_FRAME(mfn): the mfn is already present
> + * somewhere in this domain, even before being added to the
> + * m2p_override (see comment above in m2p_add_override).
> + * If there are no other entries in the m2p_override corresponding
> + * to this mfn, then remove the FOREIGN_FRAME_BIT from the p2m for
> + * the original pfn (the one shared by the frontend): the backend
> + * cannot do any IO on this page anymore because it has been
> + * unshared. Removing the FOREIGN_FRAME_BIT from the p2m entry of
> + * the original pfn causes mfn_to_pfn(mfn) to return the frontend
> + * pfn again.
> + */
> + mfn &= ~FOREIGN_FRAME_BIT;
> + ret = __get_user(pfn, &machine_to_phys_mapping[mfn]);
> + if (ret == 0 && get_phys_to_machine(pfn) == FOREIGN_FRAME(mfn) &&
> + m2p_find_override(mfn) == NULL)
> + set_phys_to_machine(pfn, mfn);
> +
> + return ret;
> +}

There is no need to keep check_duplicate_mfn separate from
remove_page_override, you can just "append" this code at the end of
remove_page_override.
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