| Message ID | 20220201090239.32067-1-jgross@suse.com (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | xen: add option to disable GNTTABOP_transfer | expand |
On 01.02.2022 10:02, Juergen Gross wrote: > The grant table operation GNTTABOP_transfer is meant to be used in > PV device backends, and it hasn't been used in Linux since the old > Xen-o-Linux days. Kind of unusual spelling of XenoLinux ;-) > --- a/xen/common/grant_table.c > +++ b/xen/common/grant_table.c > @@ -181,6 +181,7 @@ static int parse_gnttab_max_maptrack_frames(const char *arg) > > unsigned int __read_mostly opt_gnttab_max_version = GNTTAB_MAX_VERSION; > static bool __read_mostly opt_transitive_grants = true; > +static bool __read_mostly opt_grant_transfer = true; If this was conditional upon PV (with a #define to false in the opposite case), it could be __ro_after_init right away, while at the same time allowing the compiler to eliminate gnttab_transfer(). > @@ -204,6 +205,8 @@ static int __init parse_gnttab(const char *s) > } > else if ( (val = parse_boolean("transitive", s, ss)) >= 0 ) > opt_transitive_grants = val; > + else if ( (val = parse_boolean("transfer", s, ss)) >= 0 ) > + opt_grant_transfer = val; > else > rc = -EINVAL; To possibly save a further roundtrip: If the PV dependency was added above, I'd like to ask to follow the model of parse_iommu_param() here and use "#ifndef opt_grant_transfer" around the added code in favor of "#ifdef CONFIG_PV". > @@ -2233,6 +2236,9 @@ gnttab_transfer( > unsigned int max_bitsize; > struct active_grant_entry *act; > > + if ( !opt_grant_transfer ) > + return -ENOSYS; -EOPNOTSUPP please. Jan
On 03.02.22 10:10, Jan Beulich wrote: > On 01.02.2022 10:02, Juergen Gross wrote: >> The grant table operation GNTTABOP_transfer is meant to be used in >> PV device backends, and it hasn't been used in Linux since the old >> Xen-o-Linux days. > > Kind of unusual spelling of XenoLinux ;-) > >> --- a/xen/common/grant_table.c >> +++ b/xen/common/grant_table.c >> @@ -181,6 +181,7 @@ static int parse_gnttab_max_maptrack_frames(const char *arg) >> >> unsigned int __read_mostly opt_gnttab_max_version = GNTTAB_MAX_VERSION; >> static bool __read_mostly opt_transitive_grants = true; >> +static bool __read_mostly opt_grant_transfer = true; > > If this was conditional upon PV (with a #define to false in the > opposite case), it could be __ro_after_init right away, while at > the same time allowing the compiler to eliminate gnttab_transfer(). Nice idea. The other option would be to put all (or most) of gnttab_transfer() in a "#ifdef CONFIG_PV" section, allowing to remove the "#ifdef CONFIG_X86" parts in it, too. > >> @@ -204,6 +205,8 @@ static int __init parse_gnttab(const char *s) >> } >> else if ( (val = parse_boolean("transitive", s, ss)) >= 0 ) >> opt_transitive_grants = val; >> + else if ( (val = parse_boolean("transfer", s, ss)) >= 0 ) >> + opt_grant_transfer = val; >> else >> rc = -EINVAL; > > To possibly save a further roundtrip: If the PV dependency was added > above, I'd like to ask to follow the model of parse_iommu_param() > here and use "#ifndef opt_grant_transfer" around the added code in > favor of "#ifdef CONFIG_PV". Okay. > >> @@ -2233,6 +2236,9 @@ gnttab_transfer( >> unsigned int max_bitsize; >> struct active_grant_entry *act; >> >> + if ( !opt_grant_transfer ) >> + return -ENOSYS; > > -EOPNOTSUPP please. Yes, that's better. Juergen
On 03.02.2022 11:55, Juergen Gross wrote: > On 03.02.22 10:10, Jan Beulich wrote: >> On 01.02.2022 10:02, Juergen Gross wrote: >>> The grant table operation GNTTABOP_transfer is meant to be used in >>> PV device backends, and it hasn't been used in Linux since the old >>> Xen-o-Linux days. >> >> Kind of unusual spelling of XenoLinux ;-) >> >>> --- a/xen/common/grant_table.c >>> +++ b/xen/common/grant_table.c >>> @@ -181,6 +181,7 @@ static int parse_gnttab_max_maptrack_frames(const char *arg) >>> >>> unsigned int __read_mostly opt_gnttab_max_version = GNTTAB_MAX_VERSION; >>> static bool __read_mostly opt_transitive_grants = true; >>> +static bool __read_mostly opt_grant_transfer = true; >> >> If this was conditional upon PV (with a #define to false in the >> opposite case), it could be __ro_after_init right away, while at >> the same time allowing the compiler to eliminate gnttab_transfer(). > > Nice idea. The other option would be to put all (or most) of > gnttab_transfer() in a "#ifdef CONFIG_PV" section, allowing to > remove the "#ifdef CONFIG_X86" parts in it, too. Yes, sure. The downside being that then this code won't be compile- tested anymore in !PV builds. Yet keeping code visible to compilers is what we aim for elsewhere by preferring if(IS_ENABLED(...)) over #ifdef where possible. Jan
diff --git a/docs/misc/xen-command-line.pandoc b/docs/misc/xen-command-line.pandoc index 6b3da6ddc1..97ddcfa523 100644 --- a/docs/misc/xen-command-line.pandoc +++ b/docs/misc/xen-command-line.pandoc @@ -1167,9 +1167,9 @@ does not provide `VM_ENTRY_LOAD_GUEST_PAT`. Specify which console gdbstub should use. See **console**. ### gnttab -> `= List of [ max-ver:<integer>, transitive=<bool> ]` +> `= List of [ max-ver:<integer>, transitive=<bool>, transfer=<bool> ]` -> Default: `gnttab=max-ver:2,transitive` +> Default: `gnttab=max-ver:2,transitive,transfer` Control various aspects of the grant table behaviour available to guests. @@ -1178,6 +1178,9 @@ version are 1 and 2. * `transitive` Permit or disallow the use of transitive grants. Note that the use of grant table v2 without transitive grants is an ABI breakage from the guests point of view. +* `transfer` Permit or disallow the GNTTABOP_transfer operation of the +grant table hypercall. Note that disallowing GNTTABOP_transfer is an ABI +breakage from the guests point of view. The usage of gnttab v2 is not security supported on ARM platforms. diff --git a/xen/common/grant_table.c b/xen/common/grant_table.c index ed1e2fabce..d1c225e927 100644 --- a/xen/common/grant_table.c +++ b/xen/common/grant_table.c @@ -181,6 +181,7 @@ static int parse_gnttab_max_maptrack_frames(const char *arg) unsigned int __read_mostly opt_gnttab_max_version = GNTTAB_MAX_VERSION; static bool __read_mostly opt_transitive_grants = true; +static bool __read_mostly opt_grant_transfer = true; static int __init parse_gnttab(const char *s) { @@ -204,6 +205,8 @@ static int __init parse_gnttab(const char *s) } else if ( (val = parse_boolean("transitive", s, ss)) >= 0 ) opt_transitive_grants = val; + else if ( (val = parse_boolean("transfer", s, ss)) >= 0 ) + opt_grant_transfer = val; else rc = -EINVAL; @@ -2233,6 +2236,9 @@ gnttab_transfer( unsigned int max_bitsize; struct active_grant_entry *act; + if ( !opt_grant_transfer ) + return -ENOSYS; + for ( i = 0; i < count; i++ ) { bool_t okay;
The grant table operation GNTTABOP_transfer is meant to be used in PV device backends, and it hasn't been used in Linux since the old Xen-o-Linux days. Add a command line sub-option to the "gnttab" option for disabling the GNTTABOP_transfer functionality. Signed-off-by: Juergen Gross <jgross@suse.com> --- docs/misc/xen-command-line.pandoc | 7 +++++-- xen/common/grant_table.c | 6 ++++++ 2 files changed, 11 insertions(+), 2 deletions(-)