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Re: [PATCH] x86/xen: fix percpu vcpu_info allocation


  • To: Juergen Gross <jgross@xxxxxxxx>, linux-kernel@xxxxxxxxxxxxxxx, x86@xxxxxxxxxx
  • From: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
  • Date: Mon, 27 Nov 2023 09:57:49 -0500
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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
  • Delivery-date: Mon, 27 Nov 2023 14:58:25 +0000
  • List-id: Xen developer discussion <xen-devel.lists.xenproject.org>



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.


-boris


@@ -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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