linux-kernel - Re: [PATCH v2 1/2] xen/grant-table: Avoid m2p

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Message-ID: <52DAEBB1.2050405@citrix.com>
Date:	Sat, 18 Jan 2014 21:01:37 +0000
From:	Zoltan Kiss <zoltan.kiss@...rix.com>
To:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	David Vrabel <david.vrabel@...rix.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, <x86@...nel.org>,
	<xen-devel@...ts.xenproject.org>, <linux-kernel@...r.kernel.org>,
	Roger Pau Monné <roger.pau@...rix.com>,
	Jan Beulich <jbeulich@...e.com>,
	Ian Campbell <Ian.Campbell@...rix.com>
CC:	Zoltan Kiss <zoltan.kiss@...rix.com>
Subject: Re: [PATCH v2 1/2] xen/grant-table: Avoid m2p_override during mapping

On 13/01/14 19:08, Zoltan Kiss wrote:
> @@ -284,8 +287,37 @@ static int map_grant_pages(struct grant_map *map)
>   	}
>   
>   	pr_debug("map %d+%d\n", map->index, map->count);
> -	err = gnttab_map_refs(map->map_ops, use_ptemod ? map->kmap_ops : NULL,
> -			map->pages, map->count);
> +	err = gnttab_map_refs(map->map_ops, NULL, map->pages, map->count);
> +	if (err)
> +		return err;
> +
> +	if (!in_interrupt() && paravirt_get_lazy_mode() == PARAVIRT_LAZY_NONE) {
> +		arch_enter_lazy_mmu_mode();
> +		lazy = true;
> +	}
> +
> +	for (i = 0; i < map->count; i++) {
> +		/* Do not add to override if the map failed. */
> +		if (map->map_ops[i].status)
> +			continue;
> +
> +		if (map->map_ops[i].flags & GNTMAP_contains_pte) {
> +			pte = (pte_t *) (mfn_to_virt(PFN_DOWN(map->map_ops[i].host_addr)) +
> +				(map->map_ops[i].host_addr & ~PAGE_MASK));
> +			mfn = pte_mfn(*pte);
> +		} else {
> +			mfn = PFN_DOWN(map->map_ops[i].dev_bus_addr);
> +		}
> +		err = m2p_add_override(mfn,
> +				       map->pages[i],
> +				       use_ptemod ? &map->kmap_ops[i] : NULL);
> +		if (err)
> +			break;
> +	}
> +
> +	if (lazy)
> +		arch_leave_lazy_mmu_mode();
> +
>   	if (err)
>   		return err;
>   
>
This patch has a fundamental problem here: we change the pfn in 
gnttab_map_refs, then fetch it in m2p_override again, but then we have a 
different one than we need. This causes Dom0 crash. I will send a new 
version to fix that.

Zoli
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