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Re: [PATCH v1 1/1] target/riscv: Don't set write permissions on dirty PT


From: Alistair Francis
Subject: Re: [PATCH v1 1/1] target/riscv: Don't set write permissions on dirty PTEs
Date: Fri, 13 Mar 2020 15:26:41 -0700

On Thu, Mar 12, 2020 at 10:26 PM Richard Henderson
<address@hidden> wrote:
>
> On 3/12/20 3:10 PM, Alistair Francis wrote:
> >> I still think this must be a guest (or nested guest) bug related to 
> >> clearing
> >> PTE bits and failing to flush the TLB properly.
> >
> > It think so as well now. I have changed the Linux guest and Hypervisor
> > to be very aggressive with flushing but still can't get guest user
> > space working. I'll keep digging and see if I can figure out what's
> > going on.
> >
> >>
> >> I don't see how it could be a qemu tlb flushing bug.  The only primitive,
> >> sfence.vma, is quite heavy-handed and explicitly local to the thread.
> >
> > Yes, both sfence and hfence flush all TLBs, so that doesn't seem to be
> > the problem.
>
> Here's an idea: change the tlb_flush() calls to tlb_flush_all_cpus_synced().
>
> If that works, it suggests a guest interprocessor interrupt bug in the tlb
> shoot-down.

No change. I'll keep looking.

Alistair

>
>
> r~



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