Re: [PATCH] x86: kvm: use alternatives for VMCALL vs. VMMCALL if kernel text is read-only
On Mon, 22 Sep 2014, Paolo Bonzini wrote: On x86_64, kernel text mappings are mapped read-only with CONFIG_DEBUG_RODATA. In that case, KVM will fail to patch VMCALL instructions to VMMCALL as required on AMD processors. The failure mode is currently a divide-by-zero exception, which obviously is a KVM bug that has to be fixed. However, picking the right instruction between VMCALL and VMMCALL will be faster and will help if you cannot upgrade the hypervisor. -/* This instruction is vmcall. On non-VT architectures, it will generate a - * trap that we will then rewrite to the appropriate instruction. +#ifdef CONFIG_DEBUG_RODATA +#define KVM_HYPERCALL \ +ALTERNATIVE(.byte 0x0f,0x01,0xc1, .byte 0x0f,0x01,0xd9, X86_FEATURE_VMMCALL) If we can do it via a feature bit and alternatives, then why do you want to patch it manually if CONFIG_DEBUG_RODATA=n? Just because more #ifdeffery makes the code more readable? Thanks, tglx -- To unsubscribe from this list: send the line unsubscribe kvm in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH] x86: kvm: use alternatives for VMCALL vs. VMMCALL if kernel text is read-only
Il 22/09/2014 21:43, Borislav Petkov ha scritto: On x86_64, kernel text mappings are mapped read-only with CONFIG_DEBUG_RODATA. Hmm, that depends on DEBUG_KERNEL. I think you're actually talking about distro kernels which enable CONFIG_DEBUG_RODATA, right? This is for guest kernels, so it's not necessarily distro kernels. Anyone who compiles their kernel with CONFIG_DEBUG_RODATA + PV spinlocks would not be able to run it on AMD. Paolo -- To unsubscribe from this list: send the line unsubscribe kvm in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH] x86: kvm: use alternatives for VMCALL vs. VMMCALL if kernel text is read-only
On Tue, Sep 23, 2014 at 10:00:12AM +0200, Paolo Bonzini wrote: Il 22/09/2014 21:43, Borislav Petkov ha scritto: On x86_64, kernel text mappings are mapped read-only with CONFIG_DEBUG_RODATA. Hmm, that depends on DEBUG_KERNEL. I think you're actually talking about distro kernels which enable CONFIG_DEBUG_RODATA, right? This is for guest kernels, so it's not necessarily distro kernels. Anyone who compiles their kernel with CONFIG_DEBUG_RODATA + PV spinlocks would not be able to run it on AMD. I see. Yeah, so the patch makes sense to me: Acked-by: Borislav Petkov b...@suse.de Thanks. -- Regards/Gruss, Boris. Sent from a fat crate under my desk. Formatting is fine. -- -- To unsubscribe from this list: send the line unsubscribe kvm in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH] x86: kvm: use alternatives for VMCALL vs. VMMCALL if kernel text is read-only
On Mon, Sep 22, 2014 at 01:17:48PM +0200, Paolo Bonzini wrote: On x86_64, kernel text mappings are mapped read-only with CONFIG_DEBUG_RODATA. Hmm, that depends on DEBUG_KERNEL. I think you're actually talking about distro kernels which enable CONFIG_DEBUG_RODATA, right? -- Regards/Gruss, Boris. Sent from a fat crate under my desk. Formatting is fine. -- -- To unsubscribe from this list: send the line unsubscribe kvm in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
