Re: [ 056/184] KVM: x86: relax MSR_KVM_SYSTEM_TIME alignment check

[Ben Hutchings]

On Tue, 2013-06-04 at 19:22 +0200, Willy Tarreau wrote:
> 2.6.32-longterm review patch.  If anyone has any objections, please let me know.
> 
> ------------------
> 
> From: Marcelo Tosatti <mtosatti@xxxxxxxxxx>

This was fixed by commit 8f964525a121f2ff2df948dac908dcc65be21b5b
upstream.  This alternate fix avoids the need for extensive backporting.

Ben.

> RHEL5 i386 guests register non 32-byte aligned addresses:
> 
> kvm-clock: cpu 1, msr 0:3018aa5, secondary cpu clock
> kvm-clock: cpu 2, msr 0:301f8e9, secondary cpu clock
> kvm-clock: cpu 3, msr 0:302672d, secondary cpu clock
> 
> Check for an address+len that would cross page boundary
> instead.
> 
> Signed-off-by: Marcelo Tosatti <mtosatti@xxxxxxxxxx>
> [dannf: backported to Debian's 2.6.32]
> Signed-off-by: Willy Tarreau <w@xxxxxx>
> ---
>  arch/x86/kvm/x86.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index e24e9ce..79905f2 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -925,9 +925,10 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, u32 msr, u64 data)
>  		/* ...but clean it before doing the actual write */
>  		vcpu->arch.time_offset = data & ~(PAGE_MASK | 1);
>  
> -		/* Check that the address is 32-byte aligned. */
> -		if (vcpu->arch.time_offset &
> -				(sizeof(struct pvclock_vcpu_time_info) - 1))
> +		/* Check that address+len does not cross page boundary */
> +		if ((vcpu->arch.time_offset + 
> +			sizeof(struct pvclock_vcpu_time_info) - 1)
> +			& PAGE_MASK)
>  			break;
>  
>  		vcpu->arch.time_page =

-- 
Ben Hutchings
Theory and practice are closer in theory than in practice.
                                - John Levine, moderator of comp.compilers

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