Re: KVM: x86: drop alignment checks from KVM_MSR_SYSTEM_TIME address

[Gleb Natapov <gleb@redhat.com>]

On Fri, Mar 22, 2013 at 06:19:47PM -0300, Marcelo Tosatti wrote:
> 
> The alignment check is not necessary given that "KVM: x86: Convert
> MSR_KVM_SYSTEM_TIME to use gfn_to_hva_cache" (0b79459b482e85cb742) 
> uses kvm_write_guest which is able to handle data across page
> properly.
> 
It uses kvm_write_guest_cached which calls to copy_to_user() directly.
While this will not allow to overwrite page that does not belong to qemu
process, it is possible to write outside of memory slot. May be we
should use kvm_write_guest to do system time updates.

> Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
> 
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index f19ac0a..ec830fa 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -1952,10 +1952,6 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>  
>  		gpa_offset = data & ~(PAGE_MASK | 1);
>  
> -		/* Check that the address is 32-byte aligned. */
> -		if (gpa_offset & (sizeof(struct pvclock_vcpu_time_info) - 1))
> -			break;
> -
>  		if (kvm_gfn_to_hva_cache_init(vcpu->kvm,
>  		     &vcpu->arch.pv_time, data & ~1ULL))
>  			vcpu->arch.pv_time_enabled = false;

--
			Gleb.