linux-kernel - Re: [PATCH 2/2 v2] kdump,vmcoreinfo: Export the value of sme mask to vmcoreinfo

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Date:   Wed, 5 Dec 2018 18:24:07 +0800
From:   Dave Young <dyoung@...hat.com>
To:     Lianbo Jiang <lijiang@...hat.com>
Cc:     linux-kernel@...r.kernel.org, kexec@...ts.infradead.org,
        tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, x86@...nel.org,
        akpm@...ux-foundation.org, bhe@...hat.com
Subject: Re: [PATCH 2/2 v2] kdump,vmcoreinfo: Export the value of sme mask to
 vmcoreinfo

On 12/02/18 at 11:08am, Lianbo Jiang wrote:
> For AMD machine with SME feature, makedumpfile tools need to know
> whether the crash kernel was encrypted or not. If SME is enabled
> in the first kernel, the crash kernel's page table(pgd/pud/pmd/pte)
> contains the memory encryption mask, so need to remove the sme mask
> to obtain the true physical address.
> 
> Signed-off-by: Lianbo Jiang <lijiang@...hat.com>
> ---
>  arch/x86/kernel/machine_kexec_64.c | 14 ++++++++++++++
>  1 file changed, 14 insertions(+)
> 
> diff --git a/arch/x86/kernel/machine_kexec_64.c b/arch/x86/kernel/machine_kexec_64.c
> index 4c8acdfdc5a7..1860fe24117d 100644
> --- a/arch/x86/kernel/machine_kexec_64.c
> +++ b/arch/x86/kernel/machine_kexec_64.c
> @@ -352,10 +352,24 @@ void machine_kexec(struct kimage *image)
>  
>  void arch_crash_save_vmcoreinfo(void)
>  {
> +	u64 sme_mask = sme_me_mask;
> +
>  	VMCOREINFO_NUMBER(phys_base);
>  	VMCOREINFO_SYMBOL(init_top_pgt);
>  	vmcoreinfo_append_str("NUMBER(pgtable_l5_enabled)=%d\n",
>  			pgtable_l5_enabled());
> +	/*
> +	 * Currently, the local variable 'sme_mask' stores the value of
> +	 * sme_me_mask(bit 47), and also write the value of sme_mask to
> +	 * the vmcoreinfo.
> +	 * If need, the bit(sme_mask) might be redefined in the future,
> +	 * but the 'bit63' will be reserved.
> +	 * For example:
> +	 * [ misc	   ][ enc bit  ][ other misc SME info       ]
> +	 * 0000_0000_0000_0000_1000_0000_0000_0000_0000_0000_..._0000
> +	 * 63   59   55   51   47   43   39   35   31   27   ... 3
> +	 */
> +	VMCOREINFO_NUMBER(sme_mask);

#define VMCOREINFO_NUMBER(name) \
        vmcoreinfo_append_str("NUMBER(%s)=%ld\n", #name, (long)name)

VMCOREINFO_NUMBER is defined as above, so it looks questionable to add
more users of that for different data types although it may work in real
world.

A new macro like below may be better, may need to choose a better name
though:
_VMCOREINFO_NUMBER(name, format, type)
so you can pass the format specifier and data types explictly


>  
>  #ifdef CONFIG_NUMA
>  	VMCOREINFO_SYMBOL(node_data);
> -- 
> 2.17.1
> 

Thanks
Dave