From: Peter Maydell <peter.maydell@linaro.org>
To: "Alex Bennée" <alex.bennee@linaro.org>
Cc: incoming+qemu-project-qemu-11167699-3xhw7c0pviow7og92yv73e0tr-issue-404@incoming.gitlab.com,
Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>,
Richard Henderson <richard.henderson@linaro.org>,
QEMU devel list <qemu-devel@nongnu.org>,
Programmingkid <programmingkidx@gmail.com>,
Paolo Bonzini <pbonzini@redhat.com>
Subject: Re: tb_flush() calls causing long Windows XP boot times
Date: Wed, 16 Jun 2021 14:06:04 +0100 [thread overview]
Message-ID: <CAFEAcA-PafgiZWOi3TvM1VRpfKVRn+L-7bu037nLocSsXNtEzQ@mail.gmail.com> (raw)
In-Reply-To: <874kdygedv.fsf@linaro.org>
On Wed, 16 Jun 2021 at 13:53, Alex Bennée <alex.bennee@linaro.org> wrote:
>
> Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk> writes:
> > diff --git a/exec.c b/exec.c
> > index 67e520d18e..7f4074f95e 100644
> > --- a/exec.c
> > +++ b/exec.c
> > @@ -1019,14 +1019,13 @@ void tb_invalidate_phys_addr(AddressSpace *as,
> > hwaddr addr, MemTxAttrs attrs)
> >
> > static void breakpoint_invalidate(CPUState *cpu, target_ulong pc)
> > {
> > - MemTxAttrs attrs;
> > - hwaddr phys = cpu_get_phys_page_attrs_debug(cpu, pc, &attrs);
> > - int asidx = cpu_asidx_from_attrs(cpu, attrs);
> > - if (phys != -1) {
> > - /* Locks grabbed by tb_invalidate_phys_addr */
> > - tb_invalidate_phys_addr(cpu->cpu_ases[asidx].as,
> > - phys | (pc & ~TARGET_PAGE_MASK), attrs);
> > - }
> > + /*
> > + * There may not be a virtual to physical translation for the pc
> > + * right now, but there may exist cached TB for this pc.
> > + * Flush the whole TB cache to force re-translation of such TBs.
> > + * This is heavyweight, but we're debugging anyway.
> > + */
> > + tb_flush(cpu);
> > }
> > #endif
> >
> >
> > Unfortunately my x86-fu isn't really enough to understand what the
> > solution should be in this case.
>
> It's not really an x86 issue here but that we don't have any easy way of
> finding the subset of TranslationBlock's that might be affected. We can
> only query the QHT for a head address + flags. Meanwhile when there is
> an active mapping we go through the page tables
Could we do something where we zap the TBs here where there is an active
virtual-to-physical mapping for this PC, and also make a record of affected
PCs (or PC ranges) so that before we add a new entry to the
virtual-to-physical mapping we check the record to see if we actually need
to flush this TB? I think if you flush all the TLBs at this point then
you can do the "check before adding new entry" part in
tlb_set_page_with_attrs(),
but I'm not super familiar with the execution flow of TCG so that might be
wrong. Also there needs to be a point where we can discard entries from
our "dump this TB for this PC" records so they don't just grow indefinitely,
and I'm not sure what that would be.
thanks
-- PMM
next prev parent reply other threads:[~2021-06-16 13:08 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-10 12:59 tb_flush() calls causing long Windows XP boot times Programmingkid
2021-06-10 13:14 ` Peter Maydell
2021-06-10 13:24 ` Mark Cave-Ayland
2021-06-11 11:24 ` Alex Bennée
2021-06-11 15:01 ` Programmingkid
2021-06-11 17:13 ` Paolo Bonzini
2021-06-11 18:22 ` Alex Bennée
2021-06-13 14:03 ` Mark Cave-Ayland
2021-06-14 14:37 ` Alex Bennée
2021-06-15 13:58 ` Programmingkid
2021-06-16 1:58 ` Richard Henderson
2021-06-16 8:59 ` Mark Cave-Ayland
2021-06-16 12:53 ` Alex Bennée
2021-06-16 13:06 ` Peter Maydell [this message]
2021-06-16 15:30 ` Alex Bennée
2021-06-16 13:21 ` Alex Bennée
2021-06-16 12:12 ` Programmingkid
2021-06-10 13:38 ` Programmingkid
2021-06-14 22:19 ` no-reply
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