Re: [PATCH v10 21/45] x86/mm: Add support to validate memory when changing C-bit

Brijesh Singh
2022-02-21T19:54:10Z

On 2/21/22 11:41, Kirill A. Shutemov wrote:
> On Wed, Feb 16, 2022 at 10:04:57AM -0600, Brijesh Singh wrote:
>> @@ -287,6 +301,7 @@ struct x86_platform_ops {
>> struct x86_legacy_features legacy;
>> void (*set_legacy_features)(void);
>> struct x86_hyper_runtime hyper;
>> + struct x86_guest guest;
>> };
>
> I used 'cc' instead of 'guest'. 'guest' looks too generic.

I am fine with either of them.

>
> Also, I'm not sure why not to use pointer to ops struct instead of stroing
> them directly in x86_platform. Yes, it is consistent with 'hyper', but I
> don't see it as a strong argument.
>
>>
>> index b4072115c8ef..a55477a6e578 100644
>> --- a/arch/x86/mm/pat/set_memory.c
>> +++ b/arch/x86/mm/pat/set_memory.c
>> @@ -2012,8 +2012,15 @@ static int __set_memory_enc_pgtable(unsigned long addr, int numpages, bool enc)
>> */
>> cpa_flush(&cpa, !this_cpu_has(X86_FEATURE_SME_COHERENT));
>>
>> + /* Notify HV that we are about to set/clr encryption attribute. */
>> + x86_platform.guest.enc_status_change_prepare(addr, numpages, enc);
>> +
>> ret = __change_page_attr_set_clr(&cpa, 1);
>
> This doesn't cover difference in flushing requirements. Can we get it too?
>

Yes, we can work to include that too.

>>
>> + /* Notify HV that we have succesfully set/clr encryption attribute. */
>> + if (!ret)
>> + x86_platform.guest.enc_status_change_finish(addr, numpages, enc);
>> +
>
> Any particular reason you moved it above cpa_flush()? I don't think it
> makes a difference for TDX, but still.
>

It does not make any difference for the SNP as well. We can keep it
where it was.

>> /*
>> * After changing the encryption attribute, we need to flush TLBs again
>> * in case any speculative TLB caching occurred (but no need to flush
>> @@ -2023,12 +2030,6 @@ static int __set_memory_enc_pgtable(unsigned long addr, int numpages, bool enc)
>> */
>> cpa_flush(&cpa, 0);
>>
>> - /*
>> - * Notify hypervisor that a given memory range is mapped encrypted
>> - * or decrypted.
>> - */
>> - notify_range_enc_status_changed(addr, numpages, enc);
>> -
>> return ret;
>> }
>>
>> --
>> 2.25.1
>>
>