Re: [PATCH 2/2] Remove the memory encryption mask to obtain the true physical address

[lijiang <lijiang@redhat.com>]

在 2019年01月24日 06:16, Kazuhito Hagio 写道:
> On 1/22/2019 3:03 AM, Lianbo Jiang wrote:
>> For AMD machine with SME feature, if SME is enabled in the first
>> kernel, the crashed kernel's page table(pgd/pud/pmd/pte) contains
>> the memory encryption mask, so makedumpfile needs to remove the
>> memory encryption mask to obtain the true physical address.
>>
>> Signed-off-by: Lianbo Jiang <lijiang@redhat.com>
>> ---
>>  arch/x86_64.c  | 3 +++
>>  makedumpfile.c | 1 +
>>  2 files changed, 4 insertions(+)
>>
>> diff --git a/arch/x86_64.c b/arch/x86_64.c
>> index 537fb78..7651d36 100644
>> --- a/arch/x86_64.c
>> +++ b/arch/x86_64.c
>> @@ -346,6 +346,7 @@ __vtop4_x86_64(unsigned long vaddr, unsigned long pagetable)
>>  			return NOT_PADDR;
>>  		}
>>  		pud_paddr  = pgd & ENTRY_MASK;
>> +		pud_paddr = pud_paddr & ~(NUMBER(sme_mask));
>>  	}
>>
>>  	/*
>> @@ -371,6 +372,7 @@ __vtop4_x86_64(unsigned long vaddr, unsigned long pagetable)
>>  	 * Get PMD.
>>  	 */
>>  	pmd_paddr  = pud_pte & ENTRY_MASK;
>> +	pmd_paddr = pmd_paddr & ~(NUMBER(sme_mask));
>>  	pmd_paddr += pmd_index(vaddr) * sizeof(unsigned long);
>>  	if (!readmem(PADDR, pmd_paddr, &pmd_pte, sizeof pmd_pte)) {
>>  		ERRMSG("Can't get pmd_pte (pmd_paddr:%lx).\n", pmd_paddr);
>> @@ -391,6 +393,7 @@ __vtop4_x86_64(unsigned long vaddr, unsigned long pagetable)
>>  	 * Get PTE.
>>  	 */
>>  	pte_paddr  = pmd_pte & ENTRY_MASK;
>> +	pte_paddr = pte_paddr & ~(NUMBER(sme_mask));
>>  	pte_paddr += pte_index(vaddr) * sizeof(unsigned long);
>>  	if (!readmem(PADDR, pte_paddr, &pte, sizeof pte)) {
>>  		ERRMSG("Can't get pte (pte_paddr:%lx).\n", pte_paddr);
>> diff --git a/makedumpfile.c b/makedumpfile.c
>> index a03aaa1..81c7bb4 100644
>> --- a/makedumpfile.c
>> +++ b/makedumpfile.c
>> @@ -977,6 +977,7 @@ next_page:
>>  	read_size = MIN(info->page_size - PAGEOFFSET(paddr), size);
>>
>>  	pgaddr = PAGEBASE(paddr);
>> +	pgaddr = pgaddr & ~(NUMBER(sme_mask));
> 
> Since NUMBER(sme_mask) is initialized with -1 (NOT_FOUND_NUMBER),
> if the sme_mask is not in vmcoreinfo, ~(NUMBER(sme_mask)) will be 0.
> So the four lines added above need
> 
>   if (NUMBER(sme_mask) != NOT_FOUND_NUMBER)
>     ...
> 

Thank you very much for pointing out my mistake.

I will improve it and post again.

> and, what I'm wondering is whether it doesn't need to take hugepages
> into account such as this
> 
> 392         if (pmd_pte & _PAGE_PSE)        /* 2MB pages */
> 393                 return (pmd_pte & ENTRY_MASK & PMD_MASK) +
> 394                         (vaddr & ~PMD_MASK);
> "arch/x86_64.c"
> 

This is a good question. Theoretically, it should be modified accordingly for
huge pages case.

But makedumpfile still works well without this change. And i'm sure that the
huge pages are enabled in crashed kernel. This is very strange.

Thanks.
Lianbo

> Thanks,
> Kazu
> 
> 
>>  	pgbuf = cache_search(pgaddr, read_size);
>>  	if (!pgbuf) {
>>  		++cache_miss;
>> --
>> 2.17.1
>>
> 
> 

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