From: Stefano Stabellini <sstabellini@kernel.org>
To: Julien Grall <julien.grall@arm.com>
Cc: xen-devel@lists.xenproject.org,
Stefano Stabellini <sstabellini@kernel.org>,
Volodymyr Babchuk <Volodymyr_Babchuk@epam.com>
Subject: Re: [Xen-devel] [PATCH v3 20/28] xen/arm32: head: Remove 1:1 mapping as soon as it is not used
Date: Thu, 22 Aug 2019 11:17:09 -0700 (PDT) [thread overview]
Message-ID: <alpine.DEB.2.21.1908221101110.22783@sstabellini-ThinkPad-T480s> (raw)
In-Reply-To: <20190812173019.11956-21-julien.grall@arm.com>
On Mon, 12 Aug 2019, Julien Grall wrote:
> The 1:1 mapping may clash with other parts of the Xen virtual memory
> layout. At the moment, Xen is handling the clash by only creating a
> mapping to the runtime virtual address before enabling the MMU.
>
> The rest of the mappings (such as the fixmap) will be mapped after the
> MMU is enabled. However, the code doing the mapping is not safe as it
> replace mapping without using the Break-Before-Make sequence.
>
> As the 1:1 mapping can be anywhere in the memory, it is easier to remove
> all the entries added as soon as the 1:1 mapping is not used rather than
> adding the Break-Before-Make sequence everywhere.
>
> It is difficult to track where exactly the 1:1 mapping was created
> without a full rework of create_page_tables(). Instead, introduce a new
> function remove_identity_mapping() will look where is the top-level entry
> for the 1:1 mapping and remove it.
>
> The new function is only called for the boot CPU. Secondary CPUs will
> switch directly to the runtime page-tables so there are no need to
> remove the 1:1 mapping. Note that this still doesn't make the Secondary
> CPUs path safe but it is not making it worst.
>
> Signed-off-by: Julien Grall <julien.grall@arm.com>
>
> ---
> It is very likely we will need to re-introduce the 1:1 mapping to cater
> secondary CPUs boot and suspend/resume. For now, the attempt is to make
> boot CPU path fully Arm Arm compliant.
>
> Changes in v3:
> - Remove unused label
> - Avoid harcoding slots
>
> Changes in v2:
> - Patch added
> ---
> xen/arch/arm/arm32/head.S | 86 +++++++++++++++++++++++++++++++++++++----------
> 1 file changed, 69 insertions(+), 17 deletions(-)
>
> diff --git a/xen/arch/arm/arm32/head.S b/xen/arch/arm/arm32/head.S
> index 8f945d318a..34fc9ffcee 100644
> --- a/xen/arch/arm/arm32/head.S
> +++ b/xen/arch/arm/arm32/head.S
> @@ -32,6 +32,10 @@
> #define PT_UPPER(x) (PT_##x & 0xf00)
> #define PT_LOWER(x) (PT_##x & 0x0ff)
>
> +/* Convenience defines to get slot used by Xen mapping. */
> +#define XEN_FIRST_SLOT first_table_offset(XEN_VIRT_START)
> +#define XEN_SECOND_SLOT second_table_offset(XEN_VIRT_START)
> +
> #if (defined (CONFIG_EARLY_PRINTK)) && (defined (EARLY_PRINTK_INC))
> #include EARLY_PRINTK_INC
> #endif
> @@ -158,6 +162,13 @@ past_zImage:
> ldr r0, =primary_switched
> mov pc, r0
> primary_switched:
> + /*
> + * The 1:1 map may clash with other parts of the Xen virtual memory
> + * layout. As it is not used anymore, remove it completely to
> + * avoid having to worry about replacing existing mapping
> + * afterwards.
> + */
> + bl remove_identity_mapping
> bl setup_fixmap
> #ifdef CONFIG_EARLY_PRINTK
> /* Use a virtual address to access the UART. */
> @@ -474,12 +485,63 @@ enable_mmu:
> mov pc, lr
> ENDPROC(enable_mmu)
>
> -setup_fixmap:
> +/*
> + * Remove the 1:1 map for the page-tables. It is not easy to keep track
> + * where the 1:1 map was mapped, so we will look for the top-level entry
> + * exclusive to the 1:1 map and remove it.
> + *
> + * Inputs:
> + * r9 : paddr(start)
> + *
> + * Clobbers r0 - r3
> + */
> +remove_identity_mapping:
> + /* r2:r3 := invalid page-table entry */
> + mov r2, #0x0
> + mov r3, #0x0
> /*
> - * Now we can install the fixmap and dtb mappings, since we
> - * don't need the 1:1 map any more
> + * Find the first slot used. Remove the entry for the first
> + * table if the slot is not XEN_FIRST_SLOT. For slot XEN_FIRST_SLOT,
> + * the 1:1 mapping was done in the second table.
May I suggest something more similar to the arm64 version as a comment?
Something like:
"Find the first slot used. Remove the entry for the first table if the
slot is not XEN_FIRST_SLOT. In case of XEN_FIRST_SLOT, we have to look
at the second table as the slot is shared with the XEN_VIRT_START
mapping."
> */
> - dsb
> + lsr r1, r9, #FIRST_SHIFT
> + mov_w r0, LPAE_ENTRY_MASK
ldr?
> + and r1, r1, r0 /* r1 := first slot */
> + cmp r1, #XEN_FIRST_SLOT
NIT: align
> + beq 1f
> + /* It is not in slot 0, remove the entry */
> + ldr r0, =boot_pgtable /* r0 := root table */
> + lsl r1, r1, #3 /* r1 := Slot offset */
> + strd r2, r3, [r0, r1]
> + b identity_mapping_removed
> +
> +1:
> + /*
> + * Find the second slot used. Remove the entry for the first
> + * table if the slot is not XEN_SECOND_SLOT. For slot XEN_SECOND_SLOT,
> + * it means the 1:1 mapping was not created.
> + */
> + lsr r1, r9, #SECOND_SHIFT
> + mov_w r0, LPAE_ENTRY_MASK
> + and r1, r1, r0 /* r1 := second slot */
> + cmp r1, #XEN_SECOND_SLOT
> + beq identity_mapping_removed
> + /* It is not in slot 1, remove the entry */
> + ldr r0, =boot_second /* r0 := second table */
> + lsl r1, r1, #3 /* r1 := Slot offset */
> + strd r2, r3, [r0, r1]
> +
> +identity_mapping_removed:
> + /* See asm-arm/arm32/flushtlb.h for the explanation of the sequence. */
> + dsb nshst
> + mcr CP32(r0, TLBIALLH)
> + dsb nsh
> + isb
As for the arm64 patch, I would like to understand dsb ishst vs. dsb
nshst.
> + mov pc, lr
> +ENDPROC(remove_identity_mapping)
> +
> +setup_fixmap:
> #if defined(CONFIG_EARLY_PRINTK) /* Fixmap is only used by early printk */
> /* Add UART to the fixmap table */
> ldr r1, =xen_fixmap /* r1 := vaddr (xen_fixmap) */
> @@ -489,7 +551,6 @@ setup_fixmap:
> orr r2, r2, #PT_LOWER(DEV_L3) /* r2:r3 := 4K dev map including UART */
> mov r3, #0x0
> strd r2, r3, [r1, #(FIXMAP_CONSOLE*8)] /* Map it in the first fixmap's slot */
> -1:
>
> /* Map fixmap into boot_second */
> ldr r1, =boot_second /* r1 := vaddr (boot_second) */
> @@ -501,19 +562,10 @@ setup_fixmap:
> mov r4, r4, lsr #(SECOND_SHIFT - 3) /* r4 := Slot for FIXMAP(0) */
> mov r3, #0x0
> strd r2, r3, [r1, r4] /* Map it in the fixmap's slot */
> -#endif
> -
> - /*
> - * Flush the TLB in case the 1:1 mapping happens to clash with
> - * the virtual addresses used by the fixmap or DTB.
> - */
> - dsb /* Ensure any page table updates made above
> - * have occurred. */
>
> - isb
> - mcr CP32(r0, TLBIALLH) /* Flush hypervisor TLB */
> - dsb /* Ensure completion of TLB flush */
> - isb
> + /* Ensure any page table updates made above have occurred. */
> + dsb nshst
same here
> +#endif
> mov pc, lr
> ENDPROC(setup_fixmap)
>
> --
> 2.11.0
>
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next prev parent reply other threads:[~2019-08-22 18:17 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 [this message]
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 ` [Xen-devel] [PATCH v3 24/28] xen/arm: Zero BSS after the MMU and D-cache is turned on Julien Grall
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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