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SubjectRe: [patch V2 04/16] x86/tss: Fix and move VMX BUILD_BUG_ON()
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On 11/11/19 23:03, Thomas Gleixner wrote:
> The BUILD_BUG_ON(IO_BITMAP_OFFSET - 1 == 0x67) in the VMX code is bogus in
> two aspects:
>
> 1) This wants to be in generic x86 code simply to catch issues even when
> VMX is disabled in Kconfig.
>
> 2) The IO_BITMAP_OFFSET is not the right thing to check because it makes
> asssumptions about the layout of tss_struct. Nothing requires that the
> I/O bitmap is placed right after x86_tss, which is the hardware mandated
> tss structure. It pointlessly makes restrictions on the struct
> tss_struct layout.
>
> The proper thing to check is:
>
> - Offset of x86_tss in tss_struct is 0
> - Size of x86_tss == 0x68
>
> Move it to the other build time TSS checks and make it do the right thing.
>
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> ---
> V2: New patch
> ---
> arch/x86/kvm/vmx/vmx.c | 8 --------
> arch/x86/mm/cpu_entry_area.c | 8 ++++++++
> 2 files changed, 8 insertions(+), 8 deletions(-)
>
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -1338,14 +1338,6 @@ void vmx_vcpu_load_vmcs(struct kvm_vcpu
> (unsigned long)&get_cpu_entry_area(cpu)->tss.x86_tss);
> vmcs_writel(HOST_GDTR_BASE, (unsigned long)gdt); /* 22.2.4 */
>
> - /*
> - * VM exits change the host TR limit to 0x67 after a VM
> - * exit. This is okay, since 0x67 covers everything except
> - * the IO bitmap and have have code to handle the IO bitmap
> - * being lost after a VM exit.
> - */
> - BUILD_BUG_ON(IO_BITMAP_OFFSET - 1 != 0x67);
> -
> rdmsrl(MSR_IA32_SYSENTER_ESP, sysenter_esp);
> vmcs_writel(HOST_IA32_SYSENTER_ESP, sysenter_esp); /* 22.2.3 */
>
> --- a/arch/x86/mm/cpu_entry_area.c
> +++ b/arch/x86/mm/cpu_entry_area.c
> @@ -161,6 +161,14 @@ static void __init setup_cpu_entry_area(
> BUILD_BUG_ON((offsetof(struct tss_struct, x86_tss) ^
> offsetofend(struct tss_struct, x86_tss)) & PAGE_MASK);
> BUILD_BUG_ON(sizeof(struct tss_struct) % PAGE_SIZE != 0);
> + /*
> + * VMX changes the host TR limit to 0x67 after a VM exit. This is
> + * okay, since 0x67 covers the size of struct x86_hw_tss. Make sure
> + * that this is correct.
> + */
> + BUILD_BUG_ON(offsetof(struct tss_struct, x86_tss) != 0);
> + BUILD_BUG_ON(sizeof(struct x86_hw_tss) != 0x68);
> +
> cea_map_percpu_pages(&cea->tss, &per_cpu(cpu_tss_rw, cpu),
> sizeof(struct tss_struct) / PAGE_SIZE, tss_prot);
>
>
>

Acked-by: Paolo Bonzini <pbonzini@redhat.com>

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