| lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
|
Open Source and information security mailing list archives
| ||
|
Message-Id: <1421382601-46912-1-git-send-email-fenghua.yu@intel.com>
Date: Thu, 15 Jan 2015 20:30:01 -0800
From: "Fenghua Yu" <fenghua.yu@...el.com>
To: "H. Peter Anvin" <hpa@...ux.intel.com>,
"Ingo Molnar" <mingo@...e.hu>,
"Thomas Gleixner" <tglx@...utronix.de>,
"Dave Hansen" <dave.hansen@...el.com>,
"Christoph Lameter" <cl@...ux.com>,
"Glenn Williamson" <glenn.p.williamson@...el.com>
Cc: "linux-kernel" <linux-kernel@...r.kernel.org>,
"x86" <x86@...nel.org>, "Fenghua Yu" <fenghua.yu@...el.com>
Subject: [PATCH v3] X86-32: Allocate 32 bytes for pgd in PAE paging
From: Fenghua Yu <fenghua.yu@...el.com>
With more embedded systems emerging using Quark, among other things,
32-bit kernel matters again. 32-bit machine and kernel uses PAE paging,
which currently wastes at least 4K of memory per process on Linux where we
have to reserve an entire page to support a single 32-byte PGD structure.
It would be a very good thing if we could eliminate that wastage.
PAE paging is used to access more than 4GB memory on x86-32. And it is
required for NX.
In this patch, we still allocate one page for pgd for a Xen domain and 64-bit
kernel because one page pgd is assumed in these cases. But we can save memory
space by only allocating 32-byte pgd for 32-bit PAE kernel when it is not
running as a Xen domain.
Signed-off-by: Fenghua Yu <fenghua.yu@...el.com>
---
arch/x86/mm/pgtable.c | 81 +++++++++++++++++++++++++++++++++++++++++++++++++--
1 file changed, 78 insertions(+), 3 deletions(-)
diff --git a/arch/x86/mm/pgtable.c b/arch/x86/mm/pgtable.c
index 6fb6927..d223e1f 100644
--- a/arch/x86/mm/pgtable.c
+++ b/arch/x86/mm/pgtable.c
@@ -271,12 +271,87 @@ static void pgd_prepopulate_pmd(struct mm_struct *mm, pgd_t *pgd, pmd_t *pmds[])
}
}
+/*
+ * Xen paravirt assumes pgd table should be in one page. 64 bit kernel also
+ * assumes that pgd should be in one page.
+ *
+ * But kernel with PAE paging that is not running as a Xen domain
+ * only needs to allocate 32 bytes for pgd instead of one page.
+ */
+#ifdef CONFIG_X86_PAE
+
+#include <linux/slab.h>
+
+#define PGD_SIZE (PTRS_PER_PGD * sizeof(pgd_t))
+#define PGD_ALIGN 32
+
+static struct kmem_cache *pgd_cache;
+
+static int __init pgd_cache_init(void)
+{
+ /*
+ * When PAE kernel is running as a Xen domain, it does not use
+ * shared kernel pmd. And this requires a whole page for pgd.
+ */
+ if (!SHARED_KERNEL_PMD)
+ return 0;
+
+ /*
+ * when PAE kernel is not running as a Xen domain, it uses
+ * shared kernel pmd. Shared kernel pmd does not require a whole
+ * page for pgd. We are able to just allocate a 32-byte for pgd.
+ * During boot time, we create a 32-byte slab for pgd table allocation.
+ */
+ pgd_cache = kmem_cache_create("pgd_cache", PGD_SIZE, PGD_ALIGN,
+ SLAB_PANIC, NULL);
+ if (!pgd_cache)
+ return -ENOMEM;
+
+ return 0;
+}
+core_initcall(pgd_cache_init);
+
+static inline pgd_t *_pgd_alloc(void)
+{
+ /*
+ * If no SHARED_KERNEL_PMD, PAE kernel is running as a Xen domain.
+ * We allocate one page for pgd.
+ */
+ if (!SHARED_KERNEL_PMD)
+ return (pgd_t *)__get_free_page(PGALLOC_GFP);
+
+ /*
+ * Now PAE kernel is not running as a Xen domain. We can allocate
+ * a 32-byte slab for pgd to save memory space.
+ */
+ return kmem_cache_alloc(pgd_cache, PGALLOC_GFP);
+}
+
+static inline void _pgd_free(pgd_t *pgd)
+{
+ if (!SHARED_KERNEL_PMD)
+ free_page((unsigned long)pgd);
+ else
+ kmem_cache_free(pgd_cache, pgd);
+}
+#else
+static inline pgd_t *_pgd_alloc(void)
+{
+ return (pgd_t *)__get_free_page(PGALLOC_GFP);
+}
+
+static inline void _pgd_free(pgd_t *pgd)
+{
+ free_page((unsigned long)pgd);
+}
+#endif /* CONFIG_X86_PAE */
+
pgd_t *pgd_alloc(struct mm_struct *mm)
{
pgd_t *pgd;
pmd_t *pmds[PREALLOCATED_PMDS];
- pgd = (pgd_t *)__get_free_page(PGALLOC_GFP);
+ pgd = _pgd_alloc();
if (pgd == NULL)
goto out;
@@ -306,7 +381,7 @@ pgd_t *pgd_alloc(struct mm_struct *mm)
out_free_pmds:
free_pmds(pmds);
out_free_pgd:
- free_page((unsigned long)pgd);
+ _pgd_free(pgd);
out:
return NULL;
}
@@ -316,7 +391,7 @@ void pgd_free(struct mm_struct *mm, pgd_t *pgd)
pgd_mop_up_pmds(mm, pgd);
pgd_dtor(pgd);
paravirt_pgd_free(mm, pgd);
- free_page((unsigned long)pgd);
+ _pgd_free(pgd);
}
/*
--
1.8.1.2
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
Powered by blists - more mailing lists