Re: [PATCH v3 6/9] KVM: x86: Untag LAM bits when applicable

[Robert Hoo <robert.hu@linux.intel.com>]

On Wed, 2022-12-28 at 16:32 +0800, Binbin Wu wrote:
> On 12/9/2022 12:45 PM, Robert Hoo wrote
> > +#ifdef CONFIG_X86_64
> > +/* untag addr for guest, according to vCPU CR3 and CR4 settings */
> > +static inline u64 kvm_untagged_addr(u64 addr, struct kvm_vcpu
> > *vcpu)
> > +{
> > +	if (addr >> 63 == 0) {
> > +		/* User pointers */
> > +		if (kvm_read_cr3(vcpu) & X86_CR3_LAM_U57)
> > +			addr = get_canonical(addr, 57);
> 
> According to the spec, LAM_U57/LAM_SUP also performs a modified 
> canonicality check.
> 
> Why the check only be done for LAM_U48, but not for LAM_U57 and
> LAM_SUP 
> cases?
> 
Doesn't this check for LAM_U57?
And below else if branch checks LAM_U48.
And below outer else if branch checks CR4.LAM_SUP.
> 
> > +		else if (kvm_read_cr3(vcpu) & X86_CR3_LAM_U48) {
> > +			/*
> > +			 * If guest enabled 5-level paging and LAM_U48,
> > +			 * bit 47 should be 0, bit 48:56 contains meta
> > data
> > +			 * although bit 47:56 are valid 5-level address
> > +			 * bits.
> > +			 * If LAM_U48 and 4-level paging, bit47 is 0.
> > +			 */
> > +			WARN_ON(addr & _BITUL(47));
> > +			addr = get_canonical(addr, 48);
> > +		}
> > +	} else if (kvm_read_cr4(vcpu) & X86_CR4_LAM_SUP) { /*
> > Supervisor pointers */
> > +		if (kvm_read_cr4(vcpu) & X86_CR4_LA57)
> > +			addr = get_canonical(addr, 57);
> > +		else
> > +			addr = get_canonical(addr, 48);
> > +	}
> > +
> > +	return addr;
> > +}
...