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Fri, 13 Mar 2020 13:34:54 +0000 (UTC) Received: from work-vm (ovpn-117-92.ams2.redhat.com [10.36.117.92]) by smtp.corp.redhat.com (Postfix) with ESMTPS id C61215D9CA; Fri, 13 Mar 2020 13:34:53 +0000 (UTC) Date: Fri, 13 Mar 2020 13:34:51 +0000 From: "Dr. David Alan Gilbert" To: Peter Maydell Subject: Re: [PATCH] exec/rom_reset: Free rom data during inmigrate skip Message-ID: <20200313133451.GD3581@work-vm> References: <20200313123014.206828-1-dgilbert@redhat.com> MIME-Version: 1.0 In-Reply-To: User-Agent: Mutt/1.13.3 (2020-01-12) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: quoted-printable Content-Disposition: inline X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 207.211.31.120 X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Paolo Bonzini , Yan Vugenfirer , Philippe =?iso-8859-1?Q?Mathieu-Daud=E9?= , QEMU Developers Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" * Peter Maydell (peter.maydell@linaro.org) wrote: > On Fri, 13 Mar 2020 at 13:21, Peter Maydell wr= ote: > > > > On Fri, 13 Mar 2020 at 12:31, Dr. David Alan Gilbert (git) > > wrote: > > > > > > From: "Dr. David Alan Gilbert" > > > > > > Commit 355477f8c73e9 skips rom reset when we're an incoming migration > > > so as not to overwrite shared ram in the ignore-shared migration > > > optimisation. > > > However, it's got an unexpected side effect that because it skips > > > freeing the ROM data, when rom_reset gets called later on, after > > > migration (e.g. during a reboot), the ROM does get reset to the origi= nal > > > file contents. Because of seabios/x86's weird reboot process > > > this confuses a reboot into hanging after a migration. > > > > > > Fixes: 355477f8c73e9 ("migration: do not rom_reset() during incoming = migration") > > > https://bugzilla.redhat.com/show_bug.cgi?id=3D1809380 > > > > > > Signed-off-by: Dr. David Alan Gilbert > > > --- > > > hw/core/loader.c | 23 ++++++++++++++--------- > > > 1 file changed, 14 insertions(+), 9 deletions(-) > > > > > > > > QTAILQ_FOREACH(rom, &roms, next) { > > > if (rom->fw_file) { > > > continue; > > > } > > > + /* > > > + * We don't need to fill in the RAM with ROM data because we= 'll fill > > > + * the data in during the next incoming migration in all cas= es. Note > > > + * that some of those RAMs can actually be modified by the g= uest on ARM > > > + * so this is probably the only right thing to do here. > > > + */ > > > + if (runstate_check(RUN_STATE_INMIGRATE) && rom->data) { > > > + /* > > > + * Free it so that a rom_reset after migration doesn't o= verwrite a > > > + * potentially modified 'rom'. > > > + */ > > > + rom_free_data(rom); > > > > Shouldn't this condition match the condition in rom_reset() > > for when we call rom_free_data()? You want the behaviour > > on a subsequent reset to match the behaviour you'd get > > if you did a reset on the source end without the migration. >=20 > Wait, this *is* rom_reset(). Now I'm really confused. The exsiting rom_reset gets called multiple times: a) During init This actually copies the ROMs and then calls rom_free_data b) During a subsequent reboot This is mostly skipped because rom->data is now free because of the prior call to rom_free_data during (a) During an inbound migrate, (a) happens before the migration, and (b) happens during a reboot after the migration. The problem is that 355477f8c73e9 caused (a) to be skipped then when (b) happens it actually overwrites the ROM because the rom_free_data had been skipped. What I'm doing here is=20 doing the rom_free_data(..) which causes it to then skip this iteration during (a) AND causes it to skip it during (b). Dave > thanks > -- PMM >=20 -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK