Re: [Xen-devel] [PATCH 2/4] x86/hypervisor: pass flags to hypervisor_flush_tlb

[Wei Liu <wl@xxxxxxx>]

On Thu, Feb 13, 2020 at 10:29:16AM +0000, Wei Liu wrote:
> On Thu, Feb 13, 2020 at 08:48:39AM +0000, Durrant, Paul wrote:
> > > -----Original Message-----
> > > From: Roger Pau Monné <roger.pau@xxxxxxxxxx>
> > > Sent: 12 February 2020 18:01
> > > To: Wei Liu <wl@xxxxxxx>
> > > Cc: Xen Development List <xen-devel@xxxxxxxxxxxxxxxxxxxx>; Durrant, Paul
> > > <pdurrant@xxxxxxxxxxxx>; Michael Kelley <mikelley@xxxxxxxxxxxxx>; Wei Liu
> > > <liuwe@xxxxxxxxxxxxx>; Jan Beulich <jbeulich@xxxxxxxx>; Andrew Cooper
> > > <andrew.cooper3@xxxxxxxxxx>
> > > Subject: Re: [PATCH 2/4] x86/hypervisor: pass flags to
> > > hypervisor_flush_tlb
> > > 
> > > On Wed, Feb 12, 2020 at 04:09:16PM +0000, Wei Liu wrote:
> > > > Hyper-V's L0 assisted flush has fine-grained control over what gets
> > > > flushed. We need all the flags available to make the best decisions
> > > > possible.
> > > >
> > > > No functional change because Xen's implementation doesn't care about
> > > > what is passed to it.
> > > 
> > > While it's certainly fine to pass a flags field with more information,
> > > the flush flags for Xen can also contain FLUSH_CACHE, FLUSH_VCPU_STATE
> > > or FLUSH_ROOT_PGTBL, can you add an assert that those never get passed
> > > to the flush hook?
> > > 
> > > IMO we should define a mask with FLUSH_TLB, FLUSH_TLB_GLOBAL,
> > > FLUSH_VA_VALID and FLUSH_ORDER_MASK and assert that those are the only
> > > valid flags to be used for the hypervisor assisted flush hook.
> > >
> > 
> > Agreed that this should be abstracted; we certainly don't want to have
> > various bits of Xen needing to know what hypervisor it is running on
> > top of.
> 
> OK. I can introduce a FLUSH_TLB_FLAGS for all things pertaining to TLB
> -- the four things mentioned in Roger's reply.

If I'm not mistaken flush_area_mask in Roger's patch already filters out
all the unwanted flags, so my code is correct as-is.

I can add

#define FLUSH_TLB_FLAGS_MASK (FLUSH_TLB | FLUSH_TLB_GLOBAL | FLUSH_VA_VALID | \
                              FLUSH_ORDER_MASK)

and use it in flush_area_mask to replace the longer string there.

Wei.


> 
> Wei.
> 
> > 
> >   Paul
> > 
> >  
> > > Thanks, Roger.

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