linux-kernel - Re: [PATCH] KVM: VMX: use same MSR bitmaps for 32-/64-bit modes, fix MSR bitmaps for processor tracing

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Message-ID: <4a6185ee-b6db-260a-08d2-34483953f2b5@redhat.com>
Date:   Tue, 9 Jan 2018 10:35:48 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [PATCH] KVM: VMX: use same MSR bitmaps for 32-/64-bit modes, fix
 MSR bitmaps for processor tracing

On 05/01/2018 16:43, Paolo Bonzini wrote:
> KVM has a small optimization where it doesn't save/restore
> MSR_KERNEL_GS_BASE if the guest is in 32-bit mode.  However,
> this complicates the code noticeably by doubling the number of
> possible MSR bitmaps.  In addition, pt_disable_intercept_for_msr
> was only updating the "basic" MSR bitmap, because x2apic and
> x2apic_apicv are memcpy'd just once in hardware_setup.
> 
> Remove the long-mode bitmaps set, and touch all the three remaining
> bitmaps in vmx_disable_intercept_for_msr and vmx_enable_intercept_for_msr.
> 
> Fixes: 3bd1f85e893daec4f3982d1d45b6bfc0683442c4
> Cc: Luwei Kang <luwei.kang@...el.com>
> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
> ---
>  arch/x86/kvm/vmx.c | 126 ++++++++++++++++++++---------------------------------
>  1 file changed, 48 insertions(+), 78 deletions(-)

Scratch it, this patch is wrong.  You cannot change the MSR bitmaps,
they are shared across all VCPUs.

Paolo