Re: [PATCH] add tlbi=off to disable INVLPGB

[Rik van Riel]

On Fri, 2026-07-31 at 10:46 +0200, Peter Zijlstra wrote:
> On Thu, Jul 30, 2026 at 11:24:39AM -0700, Borislav Petkov wrote:
> 
> > 
> > We probably won't need to write "bcast" at all, actually, because
> > that would
> > be the default. So "tlbi=ipi" only. Yeah, that's good.
> 
> Didn't we have a case where INVLPGB was disabled due to firmware or
> something? I was thinking tlbi=broadcast could be used to force
> enable
> it or something.

I have a mini PC here that does just that.

lspcu says:
      AMD Ryzen 9 7940HS w/ Radeon 780M Graphics

That suggests the core should have INVLPGB built-in,
but it shows up as disabled in cpuid.

$ cpuid -1 | grep INVLPGB
      INVLPGB instruction                      = false
      INVLPGB supports TLB flush guest nested  = false
      max page count for INVLPGB instruction = 0x0 (0)
      INVLPGB/TLBSYNC hyperv interc enable    = false

I have not been able to find a BIOS option that
results in it being enabled.

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