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Re: [XEN PATCH v5 09/13] x86/vmx: guard access to cpu_has_vmx_* in common code
- To: Sergiy Kibrik <Sergiy_Kibrik@xxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Wed, 31 Jul 2024 14:23:56 +0200
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- Cc: Roger Pau Monné <roger.pau@xxxxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Xenia Ragiadakou <xenia.ragiadakou@xxxxxxx>, Paul Durrant <paul@xxxxxxx>, Andrew Cooper <andrew.cooper3@xxxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx
- Delivery-date: Wed, 31 Jul 2024 12:24:11 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On 30.07.2024 12:33, Sergiy Kibrik wrote:
> There're several places in common code, outside of arch/x86/hvm/vmx,
> where cpu_has_vmx_* get accessed without checking whether VMX supported first.
> These macros rely on global variables defined in vmx code, so when VMX support
> is disabled accesses to these variables turn into build failures.
>
> To overcome these failures, build-time check is done before accessing global
> variables, so that DCE would remove these variables.
>
> Signed-off-by: Sergiy Kibrik <Sergiy_Kibrik@xxxxxxxx>
> Acked-by: Paul Durrant <paul@xxxxxxx>
> CC: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> CC: Jan Beulich <jbeulich@xxxxxxxx>
> ---
> changes in v5:
> - change kconfig option name VMX -> INTEL_VMX
> - do not change .c files, only modify macros in vmcs.h
Better, yet still not going far enough, as indicated earlier:
> --- a/xen/arch/x86/include/asm/hvm/vmx/vmcs.h
> +++ b/xen/arch/x86/include/asm/hvm/vmx/vmcs.h
> @@ -300,13 +300,15 @@ extern u64 vmx_ept_vpid_cap;
> #define cpu_has_wbinvd_exiting \
> (vmx_secondary_exec_control & SECONDARY_EXEC_WBINVD_EXITING)
> #define cpu_has_vmx_virtualize_apic_accesses \
> - (vmx_secondary_exec_control & SECONDARY_EXEC_VIRTUALIZE_APIC_ACCESSES)
> + (IS_ENABLED(CONFIG_INTEL_VMX) && \
> + vmx_secondary_exec_control & SECONDARY_EXEC_VIRTUALIZE_APIC_ACCESSES)
Why does this change but the earlier cpu_has_wbinvd_exiting or ...
> #define cpu_has_vmx_tpr_shadow \
> (vmx_cpu_based_exec_control & CPU_BASED_TPR_SHADOW)
> #define cpu_has_vmx_vnmi \
> (vmx_pin_based_exec_control & PIN_BASED_VIRTUAL_NMIS)
... these two (and several more elsewhere) don't?
Jan
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