[xen staging] x86/boot: introduce module release

[patchbot@xxxxxxx]

commit 3128d7248f2ad389b8e9a3e252958cbfbd1898ee
Author:     Daniel P. Smith <dpsmith@xxxxxxxxxxxxxxxxxxxx>
AuthorDate: Fri Nov 15 08:12:00 2024 -0500
Commit:     Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
CommitDate: Mon Nov 18 16:42:48 2024 +0000

    x86/boot: introduce module release
    
    A precarious approach was used to release the pages used to hold a boot 
module.
    The precariousness stemmed from the fact that in the case of PV dom0, the
    initrd module pages may be either mapped or copied into the dom0 address 
space.
    In the former case, the PV dom0 construction code will set the size of the
    module to zero, relying on discard_initial_images() to skip any modules 
with a
    size of zero. In the latter case, the pages are freed by the PV dom0
    construction code. This freeing of pages is done so that in either case, the
    initrd variable can be reused for tracking the initrd location in dom0 
memory
    through the remaining dom0 construction code.
    
    To encapsulate the logical action of releasing a boot module, the function
    release_boot_module() is introduced along with the `released` flag added to
    boot module. The boot module flag `released` allows the tracking of when a 
boot
    module has been released by release_boot_module().
    
    As part of adopting release_boot_module() the function 
discard_initial_images()
    is renamed to free_boot_modules(), a name that better reflects the functions
    actions.
    
    Signed-off-by: Daniel P. Smith <dpsmith@xxxxxxxxxxxxxxxxxxxx>
    Reviewed-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
 xen/arch/x86/hvm/dom0_build.c       |  2 +-
 xen/arch/x86/include/asm/bootinfo.h |  2 ++
 xen/arch/x86/include/asm/setup.h    |  4 +++-
 xen/arch/x86/pv/dom0_build.c        | 27 +++++++++++++--------------
 xen/arch/x86/setup.c                | 27 +++++++++++++++------------
 5 files changed, 34 insertions(+), 28 deletions(-)

diff --git a/xen/arch/x86/hvm/dom0_build.c b/xen/arch/x86/hvm/dom0_build.c
index 35d8d6a070..b4433bed30 100644
--- a/xen/arch/x86/hvm/dom0_build.c
+++ b/xen/arch/x86/hvm/dom0_build.c
@@ -755,7 +755,7 @@ static int __init pvh_load_kernel(
     }
 
     /* Free temporary buffers. */
-    discard_initial_images();
+    free_boot_modules();
 
     if ( cmdline != NULL )
     {
diff --git a/xen/arch/x86/include/asm/bootinfo.h 
b/xen/arch/x86/include/asm/bootinfo.h
index b9c94b370d..f768763867 100644
--- a/xen/arch/x86/include/asm/bootinfo.h
+++ b/xen/arch/x86/include/asm/bootinfo.h
@@ -34,8 +34,10 @@ struct boot_module {
     /*
      * Module State Flags:
      *   relocated: indicates module has been relocated in memory.
+     *   released:  indicates module's pages have been freed.
      */
     bool relocated:1;
+    bool released:1;
 
     /*
      * A boot module may need decompressing by Xen.  Headroom is an estimate of
diff --git a/xen/arch/x86/include/asm/setup.h b/xen/arch/x86/include/asm/setup.h
index 8a415087e9..4ad4936378 100644
--- a/xen/arch/x86/include/asm/setup.h
+++ b/xen/arch/x86/include/asm/setup.h
@@ -34,13 +34,15 @@ void setup_io_bitmap(struct domain *d);
 extern struct boot_info xen_boot_info;
 
 unsigned long initial_images_nrpages(nodeid_t node);
-void discard_initial_images(void);
+void free_boot_modules(void);
 
 struct boot_module;
 void *bootstrap_map_bm(const struct boot_module *bm);
 void *bootstrap_map(const module_t *mod);
 void bootstrap_unmap(void);
 
+void release_boot_module(struct boot_module *bm);
+
 struct rangeset;
 int remove_xen_ranges(struct rangeset *r);
 
diff --git a/xen/arch/x86/pv/dom0_build.c b/xen/arch/x86/pv/dom0_build.c
index 9cf4519111..f52ede1786 100644
--- a/xen/arch/x86/pv/dom0_build.c
+++ b/xen/arch/x86/pv/dom0_build.c
@@ -649,9 +649,12 @@ static int __init dom0_construct(struct boot_info *bi, 
struct domain *d)
                 }
             memcpy(page_to_virt(page), mfn_to_virt(initrd->mod->mod_start),
                    initrd_len);
-            mpt_alloc = pfn_to_paddr(initrd->mod->mod_start);
-            init_domheap_pages(mpt_alloc,
-                               mpt_alloc + PAGE_ALIGN(initrd_len));
+            /*
+             * The initrd was copied but the initrd variable is reused in the
+             * calculations below. As to not leak the memory used for the
+             * module free at this time.
+             */
+            release_boot_module(initrd);
             initrd_mfn = mfn_x(page_to_mfn(page));
             initrd->mod->mod_start = initrd_mfn;
         }
@@ -660,18 +663,14 @@ static int __init dom0_construct(struct boot_info *bi, 
struct domain *d)
             while ( count-- )
                 if ( assign_pages(mfn_to_page(_mfn(mfn++)), 1, d, 0) )
                     BUG();
+            /*
+             * We have mapped the initrd directly into dom0, and assigned the
+             * pages. Tell the boot_module handling that we've freed it, so the
+             * memory is left alone.
+             */
+            initrd->released = true;
         }
 
-        /*
-         * 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->mod_end = 0;
-
         iommu_memory_setup(d, "initrd", mfn_to_page(_mfn(initrd_mfn)),
                            PFN_UP(initrd_len), &flush_flags);
     }
@@ -875,7 +874,7 @@ static int __init dom0_construct(struct boot_info *bi, 
struct domain *d)
     }
 
     /* Free temporary buffers. */
-    discard_initial_images();
+    free_boot_modules();
 
     /* Set up start info area. */
     si = (start_info_t *)vstartinfo_start;
diff --git a/xen/arch/x86/setup.c b/xen/arch/x86/setup.c
index 302ff61e2b..a3b4d59e80 100644
--- a/xen/arch/x86/setup.c
+++ b/xen/arch/x86/setup.c
@@ -346,27 +346,30 @@ unsigned long __init initial_images_nrpages(nodeid_t node)
     return nr;
 }
 
-void __init discard_initial_images(void) /* a.k.a. Free boot modules */
+void __init release_boot_module(struct boot_module *bm)
+{
+    uint64_t start = pfn_to_paddr(bm->mod->mod_start);
+    uint64_t size  = bm->mod->mod_end;
+
+    ASSERT(!bm->released);
+
+    init_domheap_pages(start, start + PAGE_ALIGN(size));
+
+    bm->released = true;
+}
+
+void __init free_boot_modules(void)
 {
     struct boot_info *bi = &xen_boot_info;
     unsigned int i;
 
     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;
-
-        /*
-         * 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 )
+        if ( bi->mods[i].released )
             continue;
 
-        init_domheap_pages(start, start + PAGE_ALIGN(size));
+        release_boot_module(&bi->mods[i]);
     }
-
-    bi->nr_modules = 0;
 }
 
 static void __init init_idle_domain(void)
--
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