Re: [PATCH v4 2/2] xen/m2p: use GNTTABOP_unmap_and_replace toreinstate the original mapping

From: Konrad Rzeszutek Wilk
Date: Fri Aug 09 2013 - 11:26:29 EST


On Sun, Aug 04, 2013 at 03:39:41PM +0100, Stefano Stabellini wrote:
> GNTTABOP_unmap_grant_ref unmaps a grant and replaces it with a 0
> mapping instead of reinstating the original mapping.
> Doing so separately would be racy.
>
> To unmap a grant and reinstate the original mapping atomically we use
> GNTTABOP_unmap_and_replace.
> GNTTABOP_unmap_and_replace doesn't work with GNTMAP_contains_pte, so
> don't use it for kmaps. GNTTABOP_unmap_and_replace zeroes the mapping
> passed in new_addr so we have to reinstate it, however that is a
> per-cpu mapping only used for balloon scratch pages, so we can be sure that
> it's not going to be accessed while the mapping is not valid.

This looks to be depend on a new structure, which is not in Linux kernel?
Are you missing a dependency patch?

Shouldn't we use some logic to figure out which hypercall to use if the
hypervisor does not support it?
>
> Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
> Reviewed-by: David Vrabel <david.vrabel@xxxxxxxxxx>
> CC: alex@xxxxxxxxxxx
> CC: dcrisan@xxxxxxxxxxxx
> ---
> arch/x86/xen/p2m.c | 22 +++++++++++++++-------
> drivers/xen/gntdev.c | 11 ++---------
> 2 files changed, 17 insertions(+), 16 deletions(-)
>
> diff --git a/arch/x86/xen/p2m.c b/arch/x86/xen/p2m.c
> index 95fb2aa..0d4ec35 100644
> --- a/arch/x86/xen/p2m.c
> +++ b/arch/x86/xen/p2m.c
> @@ -161,6 +161,7 @@
> #include <asm/xen/page.h>
> #include <asm/xen/hypercall.h>
> #include <asm/xen/hypervisor.h>
> +#include <xen/balloon.h>
> #include <xen/grant_table.h>
>
> #include "multicalls.h"
> @@ -967,7 +968,10 @@ int m2p_remove_override(struct page *page,
> if (kmap_op != NULL) {
> if (!PageHighMem(page)) {
> struct multicall_space mcs;
> - struct gnttab_unmap_grant_ref *unmap_op;
> + struct gnttab_unmap_and_replace *unmap_op;
> + struct page *scratch_page = get_balloon_scratch_page();
> + unsigned long scratch_page_address = (unsigned long)
> + __va(page_to_pfn(scratch_page) << PAGE_SHIFT);
>
> /*
> * It might be that we queued all the m2p grant table
> @@ -990,21 +994,25 @@ int m2p_remove_override(struct page *page,
> }
>
> mcs = xen_mc_entry(
> - sizeof(struct gnttab_unmap_grant_ref));
> + sizeof(struct gnttab_unmap_and_replace));
> unmap_op = mcs.args;
> unmap_op->host_addr = kmap_op->host_addr;
> + unmap_op->new_addr = scratch_page_address;
> unmap_op->handle = kmap_op->handle;
> - unmap_op->dev_bus_addr = 0;
>
> MULTI_grant_table_op(mcs.mc,
> - GNTTABOP_unmap_grant_ref, unmap_op, 1);
> + GNTTABOP_unmap_and_replace, unmap_op, 1);
>
> xen_mc_issue(PARAVIRT_LAZY_MMU);
>
> - set_pte_at(&init_mm, address, ptep,
> - pfn_pte(pfn, PAGE_KERNEL));
> - __flush_tlb_single(address);
> + mcs = __xen_mc_entry(0);
> + MULTI_update_va_mapping(mcs.mc, scratch_page_address,
> + pfn_pte(page_to_pfn(get_balloon_scratch_page()),
> + PAGE_KERNEL_RO), 0);
> + xen_mc_issue(PARAVIRT_LAZY_MMU);
> +
> kmap_op->host_addr = 0;
> + put_balloon_scratch_page();
> }
> }
>
> diff --git a/drivers/xen/gntdev.c b/drivers/xen/gntdev.c
> index 3c8803f..51f4c95 100644
> --- a/drivers/xen/gntdev.c
> +++ b/drivers/xen/gntdev.c
> @@ -270,19 +270,12 @@ static int map_grant_pages(struct grant_map *map)
> * with find_grant_ptes.
> */
> for (i = 0; i < map->count; i++) {
> - unsigned level;
> unsigned long address = (unsigned long)
> pfn_to_kaddr(page_to_pfn(map->pages[i]));
> - pte_t *ptep;
> - u64 pte_maddr = 0;
> BUG_ON(PageHighMem(map->pages[i]));
>
> - ptep = lookup_address(address, &level);
> - pte_maddr = arbitrary_virt_to_machine(ptep).maddr;
> - gnttab_set_map_op(&map->kmap_ops[i], pte_maddr,
> - map->flags |
> - GNTMAP_host_map |
> - GNTMAP_contains_pte,
> + gnttab_set_map_op(&map->kmap_ops[i], address,
> + map->flags | GNTMAP_host_map,
> map->grants[i].ref,
> map->grants[i].domid);
> }
> --
> 1.7.2.5
>
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/