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

[lijiang <lijiang@redhat.com>]

在 2019年01月25日 22:32, Lendacky, Thomas 写道:
> On 1/24/19 9:55 PM, dyoung@redhat.com wrote:
>> + Tom
>> On 01/25/19 at 11:06am, lijiang wrote:
>>> 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.
> 
> Might be worth creating a local variable that includes ENTRY_MASK and
> NUMBER(sme_mask) so that you make the check just once. Then use that
> variable in place of ENTRY_MASK in the remainder of the function so
> that the correct value is used throughout.
> 
> This would also cover the 5-level path which would make this future
> proof should AMD someday support 5-level paging.
> 

Thank you, Tom. Makedumpfile will cover the 5-level path in next post,
though AMD does not support 5-level paging yet.

Thanks.
Lianbo

>>>
>>>> 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.
> 
> Yes, this should also have the ~(NUMBER(sme_mask)) applied to it. You
> can probably add some debugging to see if you're hitting this case and
> whether the encryption bit (sme_mask) is set just to help understand what
> is occurring. This also goes for the 1GB page check above.  However, if
> you use my suggestion of a local variable then you should be covered.
> 
> Thanks,
> Tom
> 
>>>
>>> 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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