From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
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 original
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=1809380
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
---
hw/core/loader.c | 23 ++++++++++++++---------
1 file changed, 14 insertions(+), 9 deletions(-)
diff --git a/hw/core/loader.c b/hw/core/loader.c
index d1b78f60cd..4e583eb3bd 100644
--- a/hw/core/loader.c
+++ b/hw/core/loader.c
@@ -1119,19 +1119,24 @@ static void rom_reset(void *unused)
{
Rom *rom;
- /*
- * 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 cases. Note
- * that some of those RAMs can actually be modified by the guest on ARM
- * so this is probably the only right thing to do here.
- */
- if (runstate_check(RUN_STATE_INMIGRATE))
- return;
-
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 cases. Note
+ * that some of those RAMs can actually be modified by the guest 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 overwrite a
+ * potentially modified 'rom'.
+ */
+ rom_free_data(rom);
+ }
+
if (rom->data == NULL) {
continue;
}
--
2.24.1
On Fri, 13 Mar 2020 at 12:31, Dr. David Alan Gilbert (git)
<dgilbert@redhat.com> wrote:
>
> From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
>
> 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 original
> 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=1809380
>
> Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
> ---
> 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 cases. Note
> + * that some of those RAMs can actually be modified by the guest 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 overwrite 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.
> + }
> +
> if (rom->data == NULL) {
> continue;
> }
If you put this check above your new one you wouldn't
need to check rom->data in it. Also it would make the
loop structure better match rom_reset(), which checks
rom->fw_file first, then rom->data, then has the
condition for "do we need to call rom_free_data()".
thanks
-- PMM
On Fri, 13 Mar 2020 at 13:21, Peter Maydell <peter.maydell@linaro.org> wrote:
>
> On Fri, 13 Mar 2020 at 12:31, Dr. David Alan Gilbert (git)
> <dgilbert@redhat.com> wrote:
> >
> > From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
> >
> > 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 original
> > 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=1809380
> >
> > Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
> > ---
> > 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 cases. Note
> > + * that some of those RAMs can actually be modified by the guest 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 overwrite 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.
Wait, this *is* rom_reset(). Now I'm really confused.
thanks
-- PMM
* Peter Maydell (peter.maydell@linaro.org) wrote:
> On Fri, 13 Mar 2020 at 13:21, Peter Maydell <peter.maydell@linaro.org> wrote:
> >
> > On Fri, 13 Mar 2020 at 12:31, Dr. David Alan Gilbert (git)
> > <dgilbert@redhat.com> wrote:
> > >
> > > From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
> > >
> > > 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 original
> > > 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=1809380
> > >
> > > Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
> > > ---
> > > 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 cases. Note
> > > + * that some of those RAMs can actually be modified by the guest 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 overwrite 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.
>
> 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
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
>
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK
On Fri, 13 Mar 2020 at 13:34, Dr. David Alan Gilbert
<dgilbert@redhat.com> wrote:
>
> * Peter Maydell (peter.maydell@linaro.org) wrote:
> > On Fri, 13 Mar 2020 at 13:21, Peter Maydell <peter.maydell@linaro.org> wrote:
> > >
> > > On Fri, 13 Mar 2020 at 12:31, Dr. David Alan Gilbert (git)
> > > <dgilbert@redhat.com> wrote:
> > > >
> > > > From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
> > > >
> > > > 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 original
> > > > 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=1809380
> > > >
> > > > Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
> > > > ---
> > > > 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 cases. Note
> > > > + * that some of those RAMs can actually be modified by the guest 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 overwrite 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.
> >
> > 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
> doing the rom_free_data(..) which causes it to then skip this
> iteration during (a) AND causes it to skip it during (b).
OK, but why is your condition for when to call rom_free_data()
in this special case not the same as the condition that we
use in the normal no-migration-involved case? I would expect
those to match up.
thanks
-- PMM
* Peter Maydell (peter.maydell@linaro.org) wrote:
> On Fri, 13 Mar 2020 at 13:34, Dr. David Alan Gilbert
> <dgilbert@redhat.com> wrote:
> >
> > * Peter Maydell (peter.maydell@linaro.org) wrote:
> > > On Fri, 13 Mar 2020 at 13:21, Peter Maydell <peter.maydell@linaro.org> wrote:
> > > >
> > > > On Fri, 13 Mar 2020 at 12:31, Dr. David Alan Gilbert (git)
> > > > <dgilbert@redhat.com> wrote:
> > > > >
> > > > > From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
> > > > >
> > > > > 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 original
> > > > > 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=1809380
> > > > >
> > > > > Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
> > > > > ---
> > > > > 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 cases. Note
> > > > > + * that some of those RAMs can actually be modified by the guest 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 overwrite 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.
> > >
> > > 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
> > doing the rom_free_data(..) which causes it to then skip this
> > iteration during (a) AND causes it to skip it during (b).
>
> OK, but why is your condition for when to call rom_free_data()
> in this special case not the same as the condition that we
> use in the normal no-migration-involved case? I would expect
> those to match up.
Ah yes, I think you're right, so something like:
if (runstate_check(RUN_STATE_INMIGRATE) && rom->data && rom->isrom) {
I'll try that after lunch.
Dave
> thanks
> -- PMM
>
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK
On Fri, 13 Mar 2020 at 13:57, Dr. David Alan Gilbert
<dgilbert@redhat.com> wrote:
> Ah yes, I think you're right, so something like:
>
> if (runstate_check(RUN_STATE_INMIGRATE) && rom->data && rom->isrom) {
I think you would see the difference here for images
loaded into RAM, rather than ROM -- they need to be
reinstated on reset, because the guest can scribble
on them. So we retain the data and don't free it.
thanks
-- PMM
* Peter Maydell (peter.maydell@linaro.org) wrote:
> On Fri, 13 Mar 2020 at 13:57, Dr. David Alan Gilbert
> <dgilbert@redhat.com> wrote:
> > Ah yes, I think you're right, so something like:
> >
> > if (runstate_check(RUN_STATE_INMIGRATE) && rom->data && rom->isrom) {
>
> I think you would see the difference here for images
> loaded into RAM, rather than ROM -- they need to be
> reinstated on reset, because the guest can scribble
> on them. So we retain the data and don't free it.
Hmm, that's true; so I'm failing to skip a copy in the !isrom
case, whch the original patch needed.
So what I think we'll need is:
if (runstate_check(RUN_STATE_INMIGRATE))
{
if (rom->data && rom->isrom) {
rom_free_data(rom);
}
continue;
}
> thanks
> -- PMM
>
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK
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