linux-kernel - Re: [PATCH] x86/xen: fix percpu vcpu

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Message-ID: <69ba2a99-90f7-4d39-afc6-971b0867a1c8@oracle.com>
Date:   Mon, 27 Nov 2023 09:57:49 -0500
From:   Boris Ostrovsky <boris.ostrovsky@...cle.com>
To:     Juergen Gross <jgross@...e.com>, linux-kernel@...r.kernel.org,
        x86@...nel.org
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>, xen-devel@...ts.xenproject.org
Subject: Re: [PATCH] x86/xen: fix percpu vcpu_info allocation



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@...e.com>

Reviewed-by: Boris Ostrovsky <boris.ostrovsky@...cle.con>

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);