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Re: [PATCH] x86/xen: fix percpu vcpu_info allocation
- To: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>, x86@xxxxxxxxxx
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Mon, 27 Nov 2023 16:00:17 +0100
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- Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>, Ingo Molnar <mingo@xxxxxxxxxx>, Borislav Petkov <bp@xxxxxxxxx>, Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>, "H. Peter Anvin" <hpa@xxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx, Juergen Gross <jgross@xxxxxxxx>, linux-kernel@xxxxxxxxxxxxxxx
- Delivery-date: Mon, 27 Nov 2023 15:00:23 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 27.11.2023 15:57, Boris Ostrovsky wrote:
>
>
> On 11/24/23 2:48 AM, Juergen Gross wrote:
>> Today the percpu struct vcpu_info is allocated via DEFINE_PER_CPU(),
>> meaning that it could cross a page boundary. In this case registering
>> it with the hypervisor will fail, resulting in a panic().
>>
>> This can easily be fixed by using DEFINE_PER_CPU_ALIGNED() instead,
>> as struct vcpu_info is guaranteed to have a size of 64 bytes, matching
>> the cache line size of x86 64-bit processors (Xen doesn't support
>> 32-bit processors).
>>
>> Fixes: 5ead97c84fa7 ("xen: Core Xen implementation")
>> Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
>
> Reviewed-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
>
> although I am not sure in usefulness of BUILD_BUG_ON --- 64 bytes is part of
> ABI and hypervisor already has its own BUILD_BUG_ON for this.
I understood the check to guard against SMP_CACHE_BYTES < 64.
Jan
>> @@ -160,6 +163,7 @@ void xen_vcpu_setup(int cpu)
>> int err;
>> struct vcpu_info *vcpup;
>>
>> + BUILD_BUG_ON(sizeof(*vcpup) > SMP_CACHE_BYTES);
>> BUG_ON(HYPERVISOR_shared_info == &xen_dummy_shared_info);
>
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