From: "Pedro Falcato" <pedro.falcato@gmail.com>
To: Ard Biesheuvel <ardb@kernel.org>
Cc: devel@edk2.groups.io, Gerd Hoffmann <kraxel@redhat.com>,
Jiewen Yao <jiewen.yao@intel.com>,
Michael Brown <mcb30@ipxe.org>
Subject: Re: [edk2-devel] [RFC/RFT PATCH] OvmfPkg/IoMmuDxe: don't rely on TPLs for re-entrancy
Date: Mon, 24 Jul 2023 18:08:27 +0100 [thread overview]
Message-ID: <CAKbZUD2ZTRSWHF1O1wa_bZPOUqG6FbSy09huWJhoq_Avq1J0Ag@mail.gmail.com> (raw)
In-Reply-To: <CAMj1kXHnxHgpPuBARg=bLEJrbBu_pLZ78MvqPwrqeNhHBE=VBg@mail.gmail.com>
On Mon, Jul 24, 2023 at 3:21 PM Ard Biesheuvel <ardb@kernel.org> wrote:
>
> On Sat, 22 Jul 2023 at 00:55, Pedro Falcato <pedro.falcato@gmail.com> wrote:
> >
> > On Thu, Jul 20, 2023 at 2:46 PM Ard Biesheuvel <ardb@kernel.org> wrote:
> > >
> > > Instead of relying on raising the TPL to protect the critical sections
> > > that manipulate the global bitmask that keeps track of bounce buffer
> > > allocations, use compare-and-exchange to manage the global variable, and
> > > tweak the logic to line up with that.
> > >
> > > Given that IoMmuDxe implements a singleton protocol that is shared
> > > between multiple drivers, and considering the elaborate and confusing
> > > requirements in the UEFP spec regarding TPL levels at which protocol
> > > methods may be invoked, not relying on TPL levels at all is a more
> >
> > Really good change (I had thought of this when reading through the
> > other IoMmuDxe thread), but I'm wondering if this warrants the
> > addition of bit ops (AND, OR at least) to SynchronizationLib?
> >
>
> Thanks.
>
> Atomic AND/OR would only help on the free path in this case.
>
> > Sidenote: the compiler can detect if atomic intrinsics use the "fetch"
> > value in (fetch_or, or_fetch, etc) and thus use smaller, more
> > efficient instruction sequences (https://godbolt.org/z/zWTTWacEd). if
> > only we could use those...
> >
>
> In principle, I'd agree but these are rarely used so I'm not sure it's
> worth the effort refactoring this.
Good point, let's skip any extensive refactoring for now.
Acked-by: Pedro Falcato <pedro.falcato@gmail.com>
--
Pedro
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next prev parent reply other threads:[~2023-07-24 17:08 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-07-20 13:45 [edk2-devel] [RFC/RFT PATCH] OvmfPkg/IoMmuDxe: don't rely on TPLs for re-entrancy Ard Biesheuvel
2023-07-21 22:55 ` Pedro Falcato
2023-07-24 14:21 ` Ard Biesheuvel
2023-07-24 17:08 ` Pedro Falcato [this message]
2023-08-22 6:25 ` Gerd Hoffmann
2023-08-22 7:57 ` Ard Biesheuvel
2023-08-23 11:07 ` Gerd Hoffmann
2023-08-23 15:11 ` Ard Biesheuvel
2023-08-23 17:18 ` Gerd Hoffmann
2023-08-23 18:10 ` Pedro Falcato
2023-08-24 8:06 ` Gerd Hoffmann
2023-08-24 10:31 ` Ard Biesheuvel
2023-08-28 9:16 ` Gerd Hoffmann
2023-08-28 11:13 ` Ard Biesheuvel
2023-08-31 16:01 ` Ard Biesheuvel
2023-09-04 11:45 ` Gerd Hoffmann
2023-09-04 12:06 ` Ard Biesheuvel
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