[Xen-devel] [PATCH RFC v1 41/74] xen/pvh: do not mark the low 1MB as IO mem
From: Roger Pau Monne On PVH there's nothing special on the low 1MB Signed-off-by: Roger Pau Monné Signed-off-by: Andrew Cooper --- xen/arch/x86/mm.c | 9 +++-- 1 file changed, 7 insertions(+), 2 deletions(-) diff --git a/xen/arch/x86/mm.c b/xen/arch/x86/mm.c index f73fee225e..355e6747bb 100644 --- a/xen/arch/x86/mm.c +++ b/xen/arch/x86/mm.c @@ -122,6 +122,7 @@ #include #include #include +#include #include #include @@ -288,8 +289,12 @@ void __init arch_init_memory(void) dom_cow = domain_create(DOMID_COW, DOMCRF_dummy, 0, NULL); BUG_ON(IS_ERR(dom_cow)); -/* First 1MB of RAM is historically marked as I/O. */ -for ( i = 0; i < 0x100; i++ ) +/* + * First 1MB of RAM is historically marked as I/O. If we booted PVH, + * reclaim the space. Irrespective, leave MFN 0 as special for the sake + * of 0 being a very common default value. + */ +for ( i = 0; i < (pvh_boot ? 1 : 0x100); i++ ) share_xen_page_with_guest(mfn_to_page(_mfn(i)), dom_io, XENSHARE_writable); -- 2.11.0 ___ Xen-devel mailing list Xen-devel@lists.xenproject.org https://lists.xenproject.org/mailman/listinfo/xen-devel
Re: [Xen-devel] [PATCH RFC v1 41/74] xen/pvh: do not mark the low 1MB as IO mem
>>> On 04.01.18 at 14:05, wrote: > @@ -288,8 +289,12 @@ void __init arch_init_memory(void) > dom_cow = domain_create(DOMID_COW, DOMCRF_dummy, 0, NULL); > BUG_ON(IS_ERR(dom_cow)); > > -/* First 1MB of RAM is historically marked as I/O. */ > -for ( i = 0; i < 0x100; i++ ) > +/* > + * First 1MB of RAM is historically marked as I/O. If we booted PVH, > + * reclaim the space. Irrespective, leave MFN 0 as special for the sake > + * of 0 being a very common default value. > + */ > +for ( i = 0; i < (pvh_boot ? 1 : 0x100); i++ ) > share_xen_page_with_guest(mfn_to_page(_mfn(i)), >dom_io, XENSHARE_writable); I can see this being valid as long as there's no firmware. What doesn't become clear from neither the description nor the comment is whether this is a necessary change, or just an optimization to avoid wasting these 255 pages. Jan ___ Xen-devel mailing list Xen-devel@lists.xenproject.org https://lists.xenproject.org/mailman/listinfo/xen-devel
Re: [Xen-devel] [PATCH RFC v1 41/74] xen/pvh: do not mark the low 1MB as IO mem
On Mon, Jan 08, 2018 at 03:30:17AM -0700, Jan Beulich wrote: > >>> On 04.01.18 at 14:05, wrote: > > @@ -288,8 +289,12 @@ void __init arch_init_memory(void) > > dom_cow = domain_create(DOMID_COW, DOMCRF_dummy, 0, NULL); > > BUG_ON(IS_ERR(dom_cow)); > > > > -/* First 1MB of RAM is historically marked as I/O. */ > > -for ( i = 0; i < 0x100; i++ ) > > +/* > > + * First 1MB of RAM is historically marked as I/O. If we booted PVH, > > + * reclaim the space. Irrespective, leave MFN 0 as special for the > > sake > > + * of 0 being a very common default value. > > + */ > > +for ( i = 0; i < (pvh_boot ? 1 : 0x100); i++ ) > > share_xen_page_with_guest(mfn_to_page(_mfn(i)), > >dom_io, XENSHARE_writable); > > I can see this being valid as long as there's no firmware. What > doesn't become clear from neither the description nor the > comment is whether this is a necessary change, or just an > optimization to avoid wasting these 255 pages. It's just an optimization to not waste the low 1MiB. The shim will work equally well without this. Thanks, Roger. ___ Xen-devel mailing list Xen-devel@lists.xenproject.org https://lists.xenproject.org/mailman/listinfo/xen-devel
Re: [Xen-devel] [PATCH RFC v1 41/74] xen/pvh: do not mark the low 1MB as IO mem
>>> On 08.01.18 at 11:37, wrote: > On Mon, Jan 08, 2018 at 03:30:17AM -0700, Jan Beulich wrote: >> >>> On 04.01.18 at 14:05, wrote: >> > @@ -288,8 +289,12 @@ void __init arch_init_memory(void) >> > dom_cow = domain_create(DOMID_COW, DOMCRF_dummy, 0, NULL); >> > BUG_ON(IS_ERR(dom_cow)); >> > >> > -/* First 1MB of RAM is historically marked as I/O. */ >> > -for ( i = 0; i < 0x100; i++ ) >> > +/* >> > + * First 1MB of RAM is historically marked as I/O. If we booted PVH, >> > + * reclaim the space. Irrespective, leave MFN 0 as special for the >> > sake >> > + * of 0 being a very common default value. >> > + */ >> > +for ( i = 0; i < (pvh_boot ? 1 : 0x100); i++ ) >> > share_xen_page_with_guest(mfn_to_page(_mfn(i)), >> >dom_io, XENSHARE_writable); >> >> I can see this being valid as long as there's no firmware. What >> doesn't become clear from neither the description nor the >> comment is whether this is a necessary change, or just an >> optimization to avoid wasting these 255 pages. > > It's just an optimization to not waste the low 1MiB. The shim will > work equally well without this. Good. Please say so in the description. Jan ___ Xen-devel mailing list Xen-devel@lists.xenproject.org https://lists.xenproject.org/mailman/listinfo/xen-devel
