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From: Julien Grall <julien.grall@arm.com>
To: Stefano Stabellini <sstabellini@kernel.org>
Cc: xen-devel@lists.xenproject.org,
	Andrii Anisov <Andrii_Anisov@epam.com>,
	Oleksandr_Tyshchenko@epam.com
Subject: Re: [Xen-devel] [PATCH MM-PART3 v2 11/12] xen/arm: mm: Don't open-code Xen PT update in {set, clear}_fixmap()
Date: Thu, 13 Jun 2019 09:31:52 +0100	[thread overview]
Message-ID: <a7874b6c-08b4-28a0-cb5f-ea7f7b23e2e7@arm.com> (raw)
In-Reply-To: <alpine.DEB.2.21.1906121528260.13737@sstabellini-ThinkPad-T480s>

Hi Stefano,

On 6/12/19 11:33 PM, Stefano Stabellini wrote:
> On Tue, 14 May 2019, Julien Grall wrote:
>> {set, clear}_fixmap() are currently open-coding update to the Xen
>> page-tables. This can be avoided by using the generic helpers
>> map_pages_to_xen() and destroy_xen_mappings().
>>
>> Both function are not meant to fail for fixmap, hence the BUG_ON()
>> checking the return.
> 
> BUG_ON crashes the hypervisor even in non-DEBUG builds. Would an ASSERT
> be a better choice?
The ASSERT() would disappear in non-debug potentially leading to unknown 
consequence.

If we imagine that map_pages_to_xen() fails, then it likely means that 
mapping has not been done/removed.

As set_fixmap() does not return an error, this means that the user may 
try to access an invalid mapping and therefore crash the hypervisor.

As clear_fixmap() does not return an error, this means that subsequent 
set_fixmap() may fail because map_pages_to_xen() does not allow to 
replace valid mapping.

Ideally we would want to propagate the error, however all the call to 
the functions happen during boot. So most likely the user will 
panic/BUG_ON as you this hint something has gone really wrong and we 
don't want to continue further.

Cheers,

-- 
Julien Grall

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  reply	other threads:[~2019-06-13  8:32 UTC|newest]

Thread overview: 64+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-05-14 12:31 [PATCH MM-PART3 v2 00/12] xen/arm: Provide a generic function to update Xen PT Julien Grall
2019-05-14 12:31 ` [Xen-devel] " Julien Grall
2019-05-14 12:31 ` [PATCH MM-PART3 v2 01/12] xen/arm: lpae: Add a macro to generate offsets from an address Julien Grall
2019-05-14 12:31   ` [Xen-devel] " Julien Grall
2019-06-11 18:21   ` Stefano Stabellini
2019-06-11 18:27     ` Julien Grall
2019-05-14 12:31 ` [PATCH MM-PART3 v2 02/12] xen/arm: mm: Rename create_xen_entries() to xen_pt_update() Julien Grall
2019-05-14 12:31   ` [Xen-devel] " Julien Grall
2019-06-11 18:23   ` Stefano Stabellini
2019-05-14 12:31 ` [PATCH MM-PART3 v2 03/12] xen/arm: mm: Move out of xen_pt_update() the logic to update an entry Julien Grall
2019-05-14 12:31   ` [Xen-devel] " Julien Grall
2019-06-11 18:29   ` Stefano Stabellini
2019-05-14 12:31 ` [PATCH MM-PART3 v2 04/12] xen/arm: mm: Only increment mfn when valid in xen_pt_update Julien Grall
2019-05-14 12:31   ` [Xen-devel] " Julien Grall
2019-06-11 18:37   ` Stefano Stabellini
2019-06-11 19:56     ` [Xen-devel] Checking INVALID_MFN in mfn_add (WAS: Re: [PATCH MM-PART3 v2 04/12] xen/arm: mm: Only increment mfn when valid in xen_pt_update) Julien Grall
2019-06-11 20:24       ` Andrew Cooper
2019-06-12 12:47         ` Julien Grall
2019-06-12 15:57           ` Stefano Stabellini
2019-06-12  7:53       ` Jan Beulich
2019-05-14 12:31 ` [PATCH MM-PART3 v2 05/12] xen/arm: mm: Introduce _PAGE_PRESENT and _PAGE_POPULATE Julien Grall
2019-05-14 12:31   ` [Xen-devel] " Julien Grall
2019-06-11 22:35   ` Stefano Stabellini
2019-06-12 13:00     ` Julien Grall
2019-05-14 12:31 ` [PATCH MM-PART3 v2 06/12] xen/arm: mm: Sanity check any update of Xen page tables Julien Grall
2019-05-14 12:31   ` [Xen-devel] " Julien Grall
2019-06-12  0:10   ` Stefano Stabellini
2019-06-12 14:48     ` Julien Grall
2019-06-12 15:54       ` Stefano Stabellini
2019-06-12 15:58         ` Julien Grall
2019-05-14 12:31 ` [PATCH MM-PART3 v2 07/12] xen/arm: mm: Rework xen_pt_update_entry to avoid use xenmap_operation Julien Grall
2019-05-14 12:31   ` [Xen-devel] " Julien Grall
2019-06-12 22:22   ` Stefano Stabellini
2019-05-14 12:31 ` [PATCH MM-PART3 v2 08/12] xen/arm: mm: Remove enum xenmap_operation Julien Grall
2019-05-14 12:31   ` [Xen-devel] " Julien Grall
2019-06-11 22:38   ` Stefano Stabellini
2019-05-14 12:31 ` [PATCH MM-PART3 v2 09/12] xen/arm: mm: Use {, un}map_domain_page() to map/unmap Xen page-tables Julien Grall
2019-05-14 12:31   ` [Xen-devel] " Julien Grall
2019-06-12 22:25   ` Stefano Stabellini
2019-06-13  8:07     ` Julien Grall
2019-06-13 17:55       ` Stefano Stabellini
2019-05-14 12:31 ` [PATCH MM-PART3 v2 10/12] xen/arm: mm: Rework Xen page-tables walk during update Julien Grall
2019-05-14 12:31   ` [Xen-devel] " Julien Grall
2019-06-12 22:52   ` Stefano Stabellini
2019-06-13  8:20     ` Julien Grall
2019-06-13 17:59       ` Stefano Stabellini
2019-06-13 21:32         ` Julien Grall
2019-06-13 22:57           ` Stefano Stabellini
2019-05-14 12:31 ` [PATCH MM-PART3 v2 11/12] xen/arm: mm: Don't open-code Xen PT update in {set, clear}_fixmap() Julien Grall
2019-05-14 12:31   ` [Xen-devel] " Julien Grall
2019-06-12 22:33   ` Stefano Stabellini
2019-06-13  8:31     ` Julien Grall [this message]
2019-06-13 18:51       ` Stefano Stabellini
2019-06-13 21:21         ` Julien Grall
2019-06-13 22:55           ` Stefano Stabellini
2019-05-14 12:31 ` [PATCH MM-PART3 v2 12/12] xen/arm: mm: Remove set_pte_flags_on_range() Julien Grall
2019-05-14 12:31   ` [Xen-devel] " Julien Grall
2019-06-12 22:41   ` Stefano Stabellini
2019-06-13  8:51     ` Julien Grall
2019-06-13 18:04       ` Stefano Stabellini
2019-06-13 21:22         ` Julien Grall
2019-05-29 17:23 ` [PATCH MM-PART3 v2 00/12] xen/arm: Provide a generic function to update Xen PT Julien Grall
2019-05-29 17:23   ` [Xen-devel] " Julien Grall
2019-06-10 10:08   ` Julien Grall

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