From: Julien Grall <julien.grall@arm.com>
To: xen-devel@lists.xenproject.org
Cc: Julien Grall <julien.grall@arm.com>,
Stefano Stabellini <sstabellini@kernel.org>,
Volodymyr Babchuk <Volodymyr_Babchuk@epam.com>
Subject: [Xen-devel] [PATCH v3 24/28] xen/arm: Zero BSS after the MMU and D-cache is turned on
Date: Mon, 12 Aug 2019 18:30:15 +0100 [thread overview]
Message-ID: <20190812173019.11956-25-julien.grall@arm.com> (raw)
In-Reply-To: <20190812173019.11956-1-julien.grall@arm.com>
At the moment BSS is zeroed before the MMU and D-Cache is turned on.
In other words, the cache will be bypassed when zeroing the BSS section.
On Arm64, per the Image protocol [1], the state of the cache for BSS region
is not known because it is not part of the "loaded kernel image".
On Arm32, the boot protocol [2] does not mention anything about the
state of the cache. Therefore, it should be assumed that it is not known
for BSS region.
This means that the cache will need to be invalidated twice for the BSS
region:
1) Before zeroing to remove any dirty cache line. Otherwise they may
get evicted while zeroing and therefore overriding the value.
2) After zeroing to remove any cache line that may have been
speculated. Otherwise when turning on MMU and D-Cache, the CPU may
see old values.
At the moment, the only reason to have BSS zeroed early is because the
boot page tables are part of it. To avoid the two cache invalidations,
it would be better if the boot page tables are part of the "loaded
kernel image" and therefore be zeroed when loading the image into
memory. A good candidate is the section .data.page_aligned.
A new macro DEFINE_BOOT_PAGE_TABLE is introduced to create and mark
page-tables used before BSS is zeroed. This includes all boot_* but also
xen_fixmap as zero_bss() will print a message when earlyprintk is
enabled.
[1] linux/Documentation/arm64/booting.txt
[2] linux/Documentation/arm/Booting
Signed-off-by: Julien Grall <julien.grall@arm.com>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>
---
Changes in v3:
- Add Stefano's reviewed-by
Changes in v2:
- Add missing signed-off
- Clarify commit message
- Add arm32 parts
---
xen/arch/arm/arm32/head.S | 11 +++--------
xen/arch/arm/arm64/head.S | 7 +++----
xen/arch/arm/mm.c | 23 +++++++++++++++++------
3 files changed, 23 insertions(+), 18 deletions(-)
diff --git a/xen/arch/arm/arm32/head.S b/xen/arch/arm/arm32/head.S
index 2317fb8855..e86a9f95e7 100644
--- a/xen/arch/arm/arm32/head.S
+++ b/xen/arch/arm/arm32/head.S
@@ -153,7 +153,6 @@ past_zImage:
mov r12, #0 /* r12 := is_secondary_cpu */
bl check_cpu_mode
- bl zero_bss
bl cpu_init
bl create_page_tables
bl enable_mmu
@@ -174,6 +173,7 @@ primary_switched:
/* Use a virtual address to access the UART. */
mov_w r11, EARLY_UART_VIRTUAL_ADDRESS
#endif
+ bl zero_bss
PRINT("- Ready -\r\n")
/* Setup the arguments for start_xen and jump to C world */
mov r0, r10 /* r0 := Physical offset */
@@ -284,17 +284,12 @@ ENDPROC(check_cpu_mode)
/*
* Zero BSS
*
- * Inputs:
- * r10: Physical offset
- *
* Clobbers r0 - r3
*/
zero_bss:
PRINT("- Zero BSS -\r\n")
- ldr r0, =__bss_start /* Load start & end of bss */
- ldr r1, =__bss_end
- add r0, r0, r10 /* Apply physical offset */
- add r1, r1, r10
+ ldr r0, =__bss_start /* r0 := vaddr(__bss_start) */
+ ldr r1, =__bss_end /* r1 := vaddr(__bss_start) */
mov r2, #0
1: str r2, [r0], #4
diff --git a/xen/arch/arm/arm64/head.S b/xen/arch/arm/arm64/head.S
index a6f3aa4ee5..f2a0e1d3b0 100644
--- a/xen/arch/arm/arm64/head.S
+++ b/xen/arch/arm/arm64/head.S
@@ -309,7 +309,6 @@ real_start_efi:
mov x22, #0 /* x22 := is_secondary_cpu */
bl check_cpu_mode
- bl zero_bss
bl cpu_init
bl create_page_tables
bl enable_mmu
@@ -330,6 +329,7 @@ primary_switched:
/* Use a virtual address to access the UART. */
ldr x23, =EARLY_UART_VIRTUAL_ADDRESS
#endif
+ bl zero_bss
PRINT("- Ready -\r\n")
/* Setup the arguments for start_xen and jump to C world */
mov x0, x20 /* x0 := Physical offset */
@@ -432,7 +432,6 @@ ENDPROC(check_cpu_mode)
* Zero BSS
*
* Inputs:
- * x20: Physical offset
* x26: Do we need to zero BSS?
*
* Clobbers x0 - x3
@@ -442,8 +441,8 @@ zero_bss:
cbnz x26, skip_bss
PRINT("- Zero BSS -\r\n")
- load_paddr x0, __bss_start /* Load paddr of start & end of bss */
- load_paddr x1, __bss_end
+ ldr x0, =__bss_start /* x0 := vaddr(__bss_start) */
+ ldr x1, =__bss_end /* x1 := vaddr(__bss_start) */
1: str xzr, [x0], #8
cmp x0, x1
diff --git a/xen/arch/arm/mm.c b/xen/arch/arm/mm.c
index e1cdeaaf2f..65552da4ba 100644
--- a/xen/arch/arm/mm.c
+++ b/xen/arch/arm/mm.c
@@ -62,6 +62,17 @@ mm_printk(const char *fmt, ...) {}
} while (0);
#endif
+/*
+ * Macros to define page-tables:
+ * - DEFINE_BOOT_PAGE_TABLE is used to define page-table that are used
+ * in assembly code before BSS is zeroed.
+ * - DEFINE_PAGE_TABLE{,S} are used to define one or multiple
+ * page-tables to be used after BSS is zeroed (typically they are only used
+ * in C).
+ */
+#define DEFINE_BOOT_PAGE_TABLE(name) \
+lpae_t __aligned(PAGE_SIZE) __section(".data.page_aligned") name[LPAE_ENTRIES]
+
#define DEFINE_PAGE_TABLES(name, nr) \
lpae_t __aligned(PAGE_SIZE) name[LPAE_ENTRIES * (nr)]
@@ -90,13 +101,13 @@ lpae_t __aligned(PAGE_SIZE) name[LPAE_ENTRIES * (nr)]
* Finally, if EARLY_PRINTK is enabled then xen_fixmap will be mapped
* by the CPU once it has moved off the 1:1 mapping.
*/
-DEFINE_PAGE_TABLE(boot_pgtable);
+DEFINE_BOOT_PAGE_TABLE(boot_pgtable);
#ifdef CONFIG_ARM_64
-DEFINE_PAGE_TABLE(boot_first);
-DEFINE_PAGE_TABLE(boot_first_id);
+DEFINE_BOOT_PAGE_TABLE(boot_first);
+DEFINE_BOOT_PAGE_TABLE(boot_first_id);
#endif
-DEFINE_PAGE_TABLE(boot_second);
-DEFINE_PAGE_TABLE(boot_third);
+DEFINE_BOOT_PAGE_TABLE(boot_second);
+DEFINE_BOOT_PAGE_TABLE(boot_third);
/* Main runtime page tables */
@@ -149,7 +160,7 @@ static __initdata int xenheap_first_first_slot = -1;
*/
static DEFINE_PAGE_TABLES(xen_second, 2);
/* First level page table used for fixmap */
-DEFINE_PAGE_TABLE(xen_fixmap);
+DEFINE_BOOT_PAGE_TABLE(xen_fixmap);
/* First level page table used to map Xen itself with the XN bit set
* as appropriate. */
static DEFINE_PAGE_TABLE(xen_xenmap);
--
2.11.0
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next prev parent reply other threads:[~2019-08-13 6:48 UTC|newest]
Thread overview: 50+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-08-12 17:29 [Xen-devel] [PATCH v3 00/28] xen/arm: Rework head.S to make it more compliant with the Arm Arm Julien Grall
2019-08-12 17:29 ` [Xen-devel] [PATCH v3 01/28] xen/arm: lpae: Allow more LPAE helpers to be used in assembly Julien Grall
2019-08-22 17:07 ` Stefano Stabellini
2019-08-12 17:29 ` [Xen-devel] [PATCH v3 02/28] xen/arm64: head: Remove 1:1 mapping as soon as it is not used Julien Grall
2019-08-22 17:58 ` Stefano Stabellini
2019-08-22 18:25 ` Julien Grall
2019-08-22 18:29 ` Stefano Stabellini
2019-08-12 17:29 ` [Xen-devel] [PATCH v3 03/28] xen/arm64: head: Rework and document setup_fixmap() Julien Grall
2019-08-12 17:29 ` [Xen-devel] [PATCH v3 04/28] xen/arm64: head: Rework and document launch() Julien Grall
2019-08-12 17:29 ` [Xen-devel] [PATCH v3 05/28] xen/arm64: head: Setup TTBR_EL2 in enable_mmu() and add missing isb Julien Grall
2019-08-12 17:29 ` [Xen-devel] [PATCH v3 06/28] xen/arm64: head: Introduce a macro to get a PC-relative address of a symbol Julien Grall
2019-08-12 17:29 ` [Xen-devel] [PATCH v3 07/28] xen/arm64: head: Fix typo in the documentation on top of init_uart() Julien Grall
2019-08-22 17:08 ` Stefano Stabellini
2019-08-12 17:29 ` [Xen-devel] [PATCH v3 08/28] xen/arm32: head: Add a macro to move an immediate constant into a 32-bit register Julien Grall
2019-08-12 17:30 ` [Xen-devel] [PATCH v3 09/28] xen/arm32: head: Mark the end of subroutines with ENDPROC Julien Grall
2019-08-12 17:33 ` Julien Grall
2019-08-12 17:30 ` [Xen-devel] [PATCH v3 10/28] xen/arm32: head: Don't clobber r14/lr in the macro PRINT Julien Grall
2019-08-12 17:30 ` [Xen-devel] [PATCH v3 11/28] xen/arm32: head: Rework UART initialization on boot CPU Julien Grall
2019-08-12 17:30 ` [Xen-devel] [PATCH v3 12/28] xen/arm32: head: Introduce print_reg Julien Grall
2019-08-12 17:30 ` [Xen-devel] [PATCH v3 13/28] xen/arm32: head: Introduce distinct paths for the boot CPU and secondary CPUs Julien Grall
2019-08-22 17:11 ` Stefano Stabellini
2019-08-12 17:30 ` [Xen-devel] [PATCH v3 14/28] xen/arm32: head: Rework and document check_cpu_mode() Julien Grall
2019-08-22 17:14 ` Stefano Stabellini
2019-09-07 10:35 ` Julien Grall
2019-08-12 17:30 ` [Xen-devel] [PATCH v3 15/28] xen/arm32: head: Rework and document zero_bss() Julien Grall
2019-08-12 17:30 ` [Xen-devel] [PATCH v3 16/28] xen/arm32: head: Document create_pages_tables() Julien Grall
2019-08-12 17:30 ` [Xen-devel] [PATCH v3 17/28] xen/arm32: head: Document enable_mmu() Julien Grall
2019-08-12 17:30 ` [Xen-devel] [PATCH v3 18/28] xen/arm32: head: Move assembly switch to the runtime PT in secondary CPUs path Julien Grall
2019-08-22 17:17 ` Stefano Stabellini
2019-08-12 17:30 ` [Xen-devel] [PATCH v3 19/28] xen/arm32: head: Don't setup the fixmap on secondary CPUs Julien Grall
2019-08-12 17:30 ` [Xen-devel] [PATCH v3 20/28] xen/arm32: head: Remove 1:1 mapping as soon as it is not used Julien Grall
2019-08-22 18:17 ` Stefano Stabellini
2019-08-22 18:31 ` Julien Grall
2019-08-22 22:53 ` Stefano Stabellini
2019-08-22 23:39 ` Julien Grall
2019-08-12 17:30 ` [Xen-devel] [PATCH v3 21/28] xen/arm32: head: Rework and document setup_fixmap() Julien Grall
2019-08-12 17:30 ` [Xen-devel] [PATCH v3 22/28] xen/arm32: head: Rework and document launch() Julien Grall
2019-08-12 17:30 ` [Xen-devel] [PATCH v3 23/28] xen/arm32: head: Setup HTTBR in enable_mmu() and add missing isb Julien Grall
2019-08-22 17:15 ` Stefano Stabellini
2019-08-12 17:30 ` Julien Grall [this message]
2019-08-12 17:30 ` [Xen-devel] [PATCH v3 25/28] xen/arm64: head: Introduce macros to create table and mapping entry Julien Grall
2019-08-22 23:31 ` Stefano Stabellini
2019-08-22 23:44 ` Julien Grall
2019-08-12 17:30 ` [Xen-devel] [PATCH v3 26/28] xen/arm64: head: Use a page mapping for the 1:1 mapping in create_page_tables() Julien Grall
2019-08-24 1:16 ` Stefano Stabellini
2019-09-17 17:53 ` Julien Grall
2019-08-12 17:30 ` [Xen-devel] [PATCH v3 27/28] xen/arm32: head: Introduce macros to create table and mapping entry Julien Grall
2019-08-23 1:10 ` Stefano Stabellini
2019-08-23 9:40 ` Julien Grall
2019-08-12 17:30 ` [Xen-devel] [PATCH v3 28/28] xen/arm32: head: Use a page mapping for the 1:1 mapping in create_page_tables() Julien Grall
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