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Re: [PATCH v5] xen: make VMAP support in MMU system only
- To: Ayan Kumar Halder <ayan.kumar.halder@xxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Fri, 30 Aug 2024 11:13:07 +0200
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- Cc: Penny Zheng <penny.zheng@xxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Bertrand Marquis <bertrand.marquis@xxxxxxx>, Michal Orzel <michal.orzel@xxxxxxx>, Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, Shawn Anastasio <sanastasio@xxxxxxxxxxxxxxxxxxxxx>, Alistair Francis <alistair.francis@xxxxxxx>, Bob Eshleman <bobbyeshleman@xxxxxxxxx>, Connor Davis <connojdavis@xxxxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>, Wei Chen <wei.chen@xxxxxxx>, Julien Grall <jgrall@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- Delivery-date: Fri, 30 Aug 2024 09:13:13 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 30.08.2024 11:08, Ayan Kumar Halder wrote:
> From: Penny Zheng <penny.zheng@xxxxxxx>
>
> Introduce CONFIG_HAS_VMAP which is selected by the architectures that
> use MMU. vm_init() does not do anything if CONFIG_HAS_VMAP is not
> enabled.
>
> HAS_VMAP is widely used in ALTERNATIVE feature to remap a range of
> memory with new memory attributes. Since this is highly dependent on
> virtual address translation, we choose to make HAS_VMAP selected by
> MMU. And ALTERNATIVE depends on HAS_VMAP.
>
> At the moment, the users of HARDEN_BRANCH_PREDICTOR requires to use the
> vmap() to update the exceptions vectors. While it might be possible to
> rework the code, it is believed that speculative attackes would be
> difficult to exploit on non-MMU because the software is tightly
> controlled. So for now make HARDEN_BRANCH_PREDICTOR to depend on the
> MMU.
>
> Also took the opportunity to remove "#ifdef VMAP_VIRT_START .. endif"
> from vmap.c. Instead vmap.c is compiled when HAS_VMAP is enabled. Thus,
> HAS_VMAP is now enabled from x86, ppc and riscv architectures as all of
> them use MMU and has VMAP_VIRT_START defined.
>
> Signed-off-by: Penny Zheng <penny.zheng@xxxxxxx>
> Signed-off-by: Wei Chen <wei.chen@xxxxxxx>
> Signed-off-by: Ayan Kumar Halder <ayan.kumar.halder@xxxxxxx>
> Acked-by: Julien Grall <jgrall@xxxxxxxxxx>
Acked-by: Jan Beulich <jbeulich@xxxxxxxx>
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