On Tue, 2011-07-19 at 14:17 +0100, Jan Beulich wrote:
> Oops, $subject should have said [PATCH, v3] ...
>
> >>> On 19.07.11 at 15:16, "Jan Beulich" <JBeulich@xxxxxxxxxx> wrote:
> > With our switching away from supporting 32-bit Dom0 operation, users
> > complained that attempts (perhaps due to lack of knowledge of that
> > change) to boot the no longer privileged kernel in Dom0 resulted in
> > apparently silent failure. To make the mismatch explicit and visible,
> > add feature flags that the kernel can set to indicate operation in
> > what modes it supports. For backward compatibility, absence of both
> > feature flags is taken to indicate a kernel that may be capable of
> > operating in both modes.
Actually, since you are introducing a new interface to the feature bits
_and_ it is not possible to add these new bits to the old interface
anyway can't we just have XENFEAT_privileged and require that guest
kernels using the new interface ensure that bit correctly represents the
configuration? IOW backwards compatilibilty is ensure through the
presence/absence of XEN_ELFNOTE_SUPPORTED_FEATURES.
Ian.
> >
> > v2: Due to the way elf_xen_parse_features() worked up to now (getting
> > fixed here), adding features indications to the old, string based ELF
> > note would make the respective kernel unusable on older hypervisors.
> > For that reason, a new ELF Note is being introduced that allows
> > specifying supported features as a bit array instead (with features
> > unknown to the hypervisor simply ignored, as now also done by
> > elf_xen_parse_features(), whereas here unknown kernel-required
> > features still keep the kernel [and hence VM] from booting).
> >
> > v3: Introduce and use elf_note_numeric_array() to be forward
> > compatible (or else an old hypervisor wouldn't be able to parse kernel
> > specified features occupying more than 64 bits - thanks, Ian!).
> >
> > Signed-off-by: Jan Beulich <jbeulich@xxxxxxxxxx>
> >
> > --- a/tools/libxc/xc_dom_elfloader.c
> > +++ b/tools/libxc/xc_dom_elfloader.c
> > @@ -286,6 +286,15 @@ static int xc_dom_parse_elf_kernel(struc
> > if ( (rc = elf_xen_parse(elf, &dom->parms)) != 0 )
> > return rc;
> >
> > + if ( elf_xen_feature_get(XENFEAT_privileged, dom->parms.f_required) ||
> > + (elf_xen_feature_get(XENFEAT_privileged, dom->parms.f_supported)
> > &&
> > + !elf_xen_feature_get(XENFEAT_unprivileged,
> > dom->parms.f_supported))
> > )
> > + {
> > + xc_dom_panic(dom->xch, XC_INVALID_KERNEL, "%s: Kernel does not"
> > + " support unprivileged (DomU) operation",
> > __FUNCTION__);
> > + return -EINVAL;
> > + }
> > +
> > /* find kernel segment */
> > dom->kernel_seg.vstart = dom->parms.virt_kstart;
> > dom->kernel_seg.vend = dom->parms.virt_kend;
> > --- a/xen/arch/ia64/xen/domain.c
> > +++ b/xen/arch/ia64/xen/domain.c
> > @@ -2164,6 +2164,14 @@ int __init construct_dom0(struct domain
> > return -1;
> > }
> >
> > + if (test_bit(XENFEAT_unprivileged, parms.f_required) ||
> > + (test_bit(XENFEAT_unprivileged, parms.f_supported) &&
> > + !test_bit(XENFEAT_privileged, parms.f_supported)))
> > + {
> > + printk("Kernel does not support Dom0 operation\n");
> > + return -1;
> > + }
> > +
> > p_start = parms.virt_base;
> > pkern_start = parms.virt_kstart;
> > pkern_end = parms.virt_kend;
> > --- a/xen/arch/x86/domain_build.c
> > +++ b/xen/arch/x86/domain_build.c
> > @@ -415,6 +415,14 @@ int __init construct_dom0(
> > return -EINVAL;
> > }
> >
> > + if ( test_bit(XENFEAT_unprivileged, parms.f_required) ||
> > + (test_bit(XENFEAT_unprivileged, parms.f_supported) &&
> > + !test_bit(XENFEAT_privileged, parms.f_supported)) )
> > + {
> > + printk("Kernel does not support Dom0 operation\n");
> > + return -EINVAL;
> > + }
> > +
> > #if defined(__x86_64__)
> > if ( compat32 )
> > {
> > --- a/xen/common/kernel.c
> > +++ b/xen/common/kernel.c
> > @@ -278,7 +278,8 @@ DO(xen_version)(int cmd, XEN_GUEST_HANDL
> > switch ( fi.submap_idx )
> > {
> > case 0:
> > - fi.submap = 0;
> > + fi.submap = 1U << (IS_PRIV(current->domain) ?
> > + XENFEAT_privileged : XENFEAT_unprivileged);
> > if ( VM_ASSIST(d, VMASST_TYPE_pae_extended_cr3) )
> > fi.submap |= (1U << XENFEAT_pae_pgdir_above_4gb);
> > if ( paging_mode_translate(current->domain) )
> > --- a/xen/common/libelf/libelf-dominfo.c
> > +++ b/xen/common/libelf/libelf-dominfo.c
> > @@ -26,7 +26,9 @@ static const char *const elf_xen_feature
> > [XENFEAT_writable_descriptor_tables] = "writable_descriptor_tables",
> > [XENFEAT_auto_translated_physmap] = "auto_translated_physmap",
> > [XENFEAT_supervisor_mode_kernel] = "supervisor_mode_kernel",
> > - [XENFEAT_pae_pgdir_above_4gb] = "pae_pgdir_above_4gb"
> > + [XENFEAT_pae_pgdir_above_4gb] = "pae_pgdir_above_4gb",
> > + [XENFEAT_privileged] = "privileged",
> > + [XENFEAT_unprivileged] = "unprivileged"
> > };
> > static const int elf_xen_features =
> > sizeof(elf_xen_feature_names) / sizeof(elf_xen_feature_names[0]);
> > @@ -83,7 +85,7 @@ int elf_xen_parse_features(const char *f
> > }
> > }
> > }
> > - if ( i == elf_xen_features )
> > + if ( i == elf_xen_features && required && feature[0] == '!' )
> > return -1;
> > }
> >
> > @@ -114,6 +116,7 @@ int elf_xen_parse_note(struct elf_binary
> > [XEN_ELFNOTE_LOADER] = { "LOADER", 1},
> > [XEN_ELFNOTE_PAE_MODE] = { "PAE_MODE", 1},
> > [XEN_ELFNOTE_FEATURES] = { "FEATURES", 1},
> > + [XEN_ELFNOTE_SUPPORTED_FEATURES] = { "SUPPORTED_FEATURES", 0},
> > [XEN_ELFNOTE_BSD_SYMTAB] = { "BSD_SYMTAB", 1},
> > [XEN_ELFNOTE_SUSPEND_CANCEL] = { "SUSPEND_CANCEL", 0 },
> > [XEN_ELFNOTE_MOD_START_PFN] = { "MOD_START_PFN", 0 },
> > @@ -122,6 +125,7 @@ int elf_xen_parse_note(struct elf_binary
> >
> > const char *str = NULL;
> > uint64_t val = 0;
> > + unsigned int i;
> > int type = elf_uval(elf, note, type);
> >
> > if ( (type >= sizeof(note_desc) / sizeof(note_desc[0])) ||
> > @@ -200,6 +204,12 @@ int elf_xen_parse_note(struct elf_binary
> > return -1;
> > break;
> >
> > + case XEN_ELFNOTE_SUPPORTED_FEATURES:
> > + for ( i = 0; i < XENFEAT_NR_SUBMAPS; ++i )
> > + parms->f_supported[i] |= elf_note_numeric_array(
> > + elf, note, sizeof(*parms->f_supported), i);
> > + break;
> > +
> > }
> > return 0;
> > }
> > --- a/xen/common/libelf/libelf-tools.c
> > +++ b/xen/common/libelf/libelf-tools.c
> > @@ -227,6 +227,27 @@ uint64_t elf_note_numeric(struct elf_bin
> > return 0;
> > }
> > }
> > +
> > +uint64_t elf_note_numeric_array(struct elf_binary *elf, const elf_note
> > *note,
> > + unsigned int unitsz, unsigned int idx)
> > +{
> > + const void *desc = elf_note_desc(elf, note);
> > + int descsz = elf_uval(elf, note, descsz);
> > +
> > + if ( descsz % unitsz || idx >= descsz / unitsz )
> > + return 0;
> > + switch (unitsz)
> > + {
> > + case 1:
> > + case 2:
> > + case 4:
> > + case 8:
> > + return elf_access_unsigned(elf, desc, idx * unitsz, unitsz);
> > + default:
> > + return 0;
> > + }
> > +}
> > +
> > const elf_note *elf_note_next(struct elf_binary *elf, const elf_note *
> > note)
> > {
> > int namesz = (elf_uval(elf, note, namesz) + 3) & ~3;
> > --- a/xen/include/public/elfnote.h
> > +++ b/xen/include/public/elfnote.h
> > @@ -179,9 +179,22 @@
> > #define XEN_ELFNOTE_MOD_START_PFN 16
> >
> > /*
> > + * The features supported by this kernel (numeric).
> > + *
> > + * Other than XEN_ELFNOTE_FEATURES on pre-4.2 Xen, this note allows a
> > + * kernel to specify support for features that older hypervisors don't
> > + * know about. The set of features 4.2 and newer hypervisors will
> > + * consider supported by the kernel is the combination of the sets
> > + * specified through this and the string note.
> > + *
> > + * LEGACY: FEATURES
> > + */
> > +#define XEN_ELFNOTE_SUPPORTED_FEATURES 17
> > +
> > +/*
> > * The number of the highest elfnote defined.
> > */
> > -#define XEN_ELFNOTE_MAX XEN_ELFNOTE_MOD_START_PFN
> > +#define XEN_ELFNOTE_MAX XEN_ELFNOTE_SUPPORTED_FEATURES
> >
> > /*
> > * System information exported through crash notes.
> > --- a/xen/include/public/features.h
> > +++ b/xen/include/public/features.h
> > @@ -75,7 +75,13 @@
> > #define XENFEAT_hvm_safe_pvclock 9
> >
> > /* x86: pirq can be used by HVM guests */
> > -#define XENFEAT_hvm_pirqs 10
> > +#define XENFEAT_hvm_pirqs 10
> > +
> > +/* privileged operation is supported */
> > +#define XENFEAT_privileged 11
> > +
> > +/* un-privileged operation is supported */
> > +#define XENFEAT_unprivileged 12
> >
> > #define XENFEAT_NR_SUBMAPS 1
> >
> > --- a/xen/include/xen/libelf.h
> > +++ b/xen/include/xen/libelf.h
> > @@ -179,6 +179,8 @@ const elf_sym *elf_sym_by_index(struct e
> > const char *elf_note_name(struct elf_binary *elf, const elf_note * note);
> > const void *elf_note_desc(struct elf_binary *elf, const elf_note * note);
> > uint64_t elf_note_numeric(struct elf_binary *elf, const elf_note * note);
> > +uint64_t elf_note_numeric_array(struct elf_binary *, const elf_note *,
> > + unsigned int unitsz, unsigned int idx);
> > const elf_note *elf_note_next(struct elf_binary *elf, const elf_note *
> > note);
> >
> > int elf_is_elfbinary(const void *image);
>
>
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