| Message ID | 20241024160340.1012474-1-andrew.cooper3@citrix.com (mailing list archive) |
|---|---|
| State | New |
| Headers | show |
| Series | [v2] x86/boot: Explain how discard_initial_images() works | expand |
On 10/24/24 12:03, Andrew Cooper wrote: > discard_initial_images() only works because init_domheap_pages() with ps==pe > is a no-op. > > In dom0_construct(), explaining the significance of setting the initrd length > to 0, and put an explicit check in discard_initial_images(). > > No functional change. > > Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com> > --- > CC: Jan Beulich <JBeulich@suse.com> > CC: Roger Pau Monné <roger.pau@citrix.com> > CC: Daniel Smith <dpsmith@apertussolutions.com> Reviewed-by: Daniel P. Smith <dpsmith@apertussolutions.com>
On 24.10.2024 18:03, Andrew Cooper wrote: > discard_initial_images() only works because init_domheap_pages() with ps==pe > is a no-op. And intentionally so. Hence why I don't mind ... > In dom0_construct(), explaining the significance of setting the initrd length > to 0, and put an explicit check in discard_initial_images(). ... the extra conditional, I also don't really see why we would strictly need it. Jan
diff --git a/xen/arch/x86/pv/dom0_build.c b/xen/arch/x86/pv/dom0_build.c index cdae17b27654..cc882bee61c3 100644 --- a/xen/arch/x86/pv/dom0_build.c +++ b/xen/arch/x86/pv/dom0_build.c @@ -641,6 +641,15 @@ static int __init dom0_construct(struct domain *d, if ( assign_pages(mfn_to_page(_mfn(mfn++)), 1, d, 0) ) BUG(); } + + /* + * We have either: + * - Mapped the initrd directly into dom0, or + * - Copied it and freed the module. + * + * Either way, tell discard_initial_images() to not free it a second + * time. + */ initrd->mod_end = 0; iommu_memory_setup(d, "initrd", mfn_to_page(_mfn(initrd_mfn)), diff --git a/xen/arch/x86/setup.c b/xen/arch/x86/setup.c index 511cf5b97909..177f4024abca 100644 --- a/xen/arch/x86/setup.c +++ b/xen/arch/x86/setup.c @@ -340,7 +340,7 @@ unsigned long __init initial_images_nrpages(nodeid_t node) return nr; } -void __init discard_initial_images(void) +void __init discard_initial_images(void) /* a.k.a. Free boot modules */ { struct boot_info *bi = &xen_boot_info; unsigned int i; @@ -348,9 +348,16 @@ void __init discard_initial_images(void) for ( i = 0; i < bi->nr_modules; ++i ) { uint64_t start = pfn_to_paddr(bi->mods[i].mod->mod_start); + uint64_t size = bi->mods[i].mod->mod_end; - init_domheap_pages(start, - start + PAGE_ALIGN(bi->mods[i].mod->mod_end)); + /* + * Sometimes the initrd is mapped, rather than copied, into dom0. + * Size being 0 is how we're instructed to leave the module alone. + */ + if ( size == 0 ) + continue; + + init_domheap_pages(start, start + PAGE_ALIGN(size)); } bi->nr_modules = 0;
discard_initial_images() only works because init_domheap_pages() with ps==pe is a no-op. In dom0_construct(), explaining the significance of setting the initrd length to 0, and put an explicit check in discard_initial_images(). No functional change. Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com> --- CC: Jan Beulich <JBeulich@suse.com> CC: Roger Pau Monné <roger.pau@citrix.com> CC: Daniel Smith <dpsmith@apertussolutions.com> v2: * Strip down to just the explanation, and merge into HL series. --- xen/arch/x86/pv/dom0_build.c | 9 +++++++++ xen/arch/x86/setup.c | 13 ++++++++++--- 2 files changed, 19 insertions(+), 3 deletions(-)