Re: [PATCH] x86: Implement Linear Address Masking support

[Kirill A. Shutemov]

On Thu, Apr 07, 2022 at 06:38:40PM +0200, Paolo Bonzini wrote:
> On 4/7/22 17:27, Kirill A. Shutemov wrote:
> > On Thu, Apr 07, 2022 at 07:28:54AM -0700, Richard Henderson wrote:
> > > On 4/7/22 06:18, Kirill A. Shutemov wrote:
> > > > > The new hook is incorrect, in that it doesn't apply to addresses along
> > > > > the tlb fast path.
> > > > 
> > > > I'm not sure what you mean by that. tlb_hit() mechanics works. We strip
> > > > the tag bits before tlb lookup.
> > > > 
> > > > Could you elaborate?
> > > 
> > > The fast path does not clear the bits, so you enter the slow path before 
> > > you
> > > get to clearing the bits.  You've lost most of the advantage of the tlb
> > > already.
> > 
> > Sorry for my ignorance, but what do you mean by fast path here?
> 
> The fast path is the TLB lookup code that is generated by the JIT compiler.
> If the TLB hits, the memory access doesn't go through any C code.  I think
> tagged addresses always fail the fast path in your patch.

Ah. Got it.

Could you point me to the key code area relevant to the topic? I'm not
familiar with the JIT side of QEMU.

-- 
 Kirill A. Shutemov