linux-kernel - Re: [PATCH v17 08/15] arm64: kexec: configure EL2 vectors for kexec

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Date:   Wed, 29 Sep 2021 13:35:13 +0100
From:   Will Deacon <will@...nel.org>
To:     Pasha Tatashin <pasha.tatashin@...een.com>
Cc:     jmorris@...ei.org, sashal@...nel.org, ebiederm@...ssion.com,
        kexec@...ts.infradead.org, linux-kernel@...r.kernel.org,
        corbet@....net, catalin.marinas@....com,
        linux-arm-kernel@...ts.infradead.org, maz@...nel.org,
        james.morse@....com, vladimir.murzin@....com,
        matthias.bgg@...il.com, linux-mm@...ck.org, mark.rutland@....com,
        steve.capper@....com, rfontana@...hat.com, tglx@...utronix.de,
        selindag@...il.com, tyhicks@...ux.microsoft.com,
        kernelfans@...il.com, akpm@...ux-foundation.org,
        madvenka@...ux.microsoft.com
Subject: Re: [PATCH v17 08/15] arm64: kexec: configure EL2 vectors for kexec

On Thu, Sep 16, 2021 at 07:13:18PM -0400, Pasha Tatashin wrote:
> If we have a EL2 mode without VHE, the EL2 vectors are needed in order
> to switch to EL2 and jump to new world with hypervisor privileges.
> 
> In preparation to MMU enabled relocation, configure our EL2 table now.
> 
> Kexec uses #HVC_SOFT_RESTART to branch to the new world, so extend
> el1_sync vector that is provided by trans_pgd_copy_el2_vectors() to
> support this case.
> 
> Signed-off-by: Pasha Tatashin <pasha.tatashin@...een.com>
> ---
>  arch/arm64/Kconfig                |  2 +-
>  arch/arm64/include/asm/kexec.h    |  1 +
>  arch/arm64/kernel/asm-offsets.c   |  1 +
>  arch/arm64/kernel/machine_kexec.c | 31 +++++++++++++++++++++++++++++++
>  arch/arm64/mm/trans_pgd-asm.S     |  9 ++++++++-
>  5 files changed, 42 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
> index 5c7ae4c3954b..552a057b40af 100644
> --- a/arch/arm64/Kconfig
> +++ b/arch/arm64/Kconfig
> @@ -1135,7 +1135,7 @@ config CRASH_DUMP
>  
>  config TRANS_TABLE
>  	def_bool y
> -	depends on HIBERNATION
> +	depends on HIBERNATION || KEXEC_CORE
>  
>  config XEN_DOM0
>  	def_bool y
> diff --git a/arch/arm64/include/asm/kexec.h b/arch/arm64/include/asm/kexec.h
> index 00dbcc71aeb2..753a1c398898 100644
> --- a/arch/arm64/include/asm/kexec.h
> +++ b/arch/arm64/include/asm/kexec.h
> @@ -96,6 +96,7 @@ struct kimage_arch {
>  	void *dtb;
>  	phys_addr_t dtb_mem;
>  	phys_addr_t kern_reloc;
> +	phys_addr_t el2_vectors;
>  };
>  
>  #ifdef CONFIG_KEXEC_FILE
> diff --git a/arch/arm64/kernel/asm-offsets.c b/arch/arm64/kernel/asm-offsets.c
> index 1d3319c7518e..6a2b8b1a4872 100644
> --- a/arch/arm64/kernel/asm-offsets.c
> +++ b/arch/arm64/kernel/asm-offsets.c
> @@ -174,6 +174,7 @@ int main(void)
>  #endif
>  #ifdef CONFIG_KEXEC_CORE
>    DEFINE(KIMAGE_ARCH_DTB_MEM,		offsetof(struct kimage, arch.dtb_mem));
> +  DEFINE(KIMAGE_ARCH_EL2_VECTORS,	offsetof(struct kimage, arch.el2_vectors));
>    DEFINE(KIMAGE_HEAD,			offsetof(struct kimage, head));
>    DEFINE(KIMAGE_START,			offsetof(struct kimage, start));
>    BLANK();
> diff --git a/arch/arm64/kernel/machine_kexec.c b/arch/arm64/kernel/machine_kexec.c
> index e210b19592c6..59a4b4172b68 100644
> --- a/arch/arm64/kernel/machine_kexec.c
> +++ b/arch/arm64/kernel/machine_kexec.c
> @@ -21,6 +21,7 @@
>  #include <asm/mmu.h>
>  #include <asm/mmu_context.h>
>  #include <asm/page.h>
> +#include <asm/trans_pgd.h>
>  
>  #include "cpu-reset.h"
>  
> @@ -43,7 +44,9 @@ static void _kexec_image_info(const char *func, int line,
>  	pr_debug("    start:       %lx\n", kimage->start);
>  	pr_debug("    head:        %lx\n", kimage->head);
>  	pr_debug("    nr_segments: %lu\n", kimage->nr_segments);
> +	pr_debug("    dtb_mem: %pa\n", &kimage->arch.dtb_mem);
>  	pr_debug("    kern_reloc: %pa\n", &kimage->arch.kern_reloc);
> +	pr_debug("    el2_vectors: %pa\n", &kimage->arch.el2_vectors);
>  
>  	for (i = 0; i < kimage->nr_segments; i++) {
>  		pr_debug("      segment[%lu]: %016lx - %016lx, 0x%lx bytes, %lu pages\n",
> @@ -143,9 +146,27 @@ static void kexec_segment_flush(const struct kimage *kimage)
>  	}
>  }
>  
> +/* Allocates pages for kexec page table */
> +static void *kexec_page_alloc(void *arg)
> +{
> +	struct kimage *kimage = (struct kimage *)arg;
> +	struct page *page = kimage_alloc_control_pages(kimage, 0);
> +
> +	if (!page)
> +		return NULL;
> +
> +	memset(page_address(page), 0, PAGE_SIZE);

Hmm, I think we might be missing barriers here to ensure that the zeroes
are visible to the page-table walker before we plumb the page into the
page-table.

Usually, that's taken care of by the smp_wmb() in __pXX_alloc() but I
can't see that here. Is it hiding?

Will