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

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Date:   Mon, 21 Feb 2022 13:54:03 -0600
From:   Brijesh Singh <brijesh.singh@....com>
To:     "Kirill A. Shutemov" <kirill@...temov.name>
Cc:     brijesh.singh@....com, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        linux-efi@...r.kernel.org, platform-driver-x86@...r.kernel.org,
        linux-coco@...ts.linux.dev, linux-mm@...ck.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Joerg Roedel <jroedel@...e.de>,
        Tom Lendacky <thomas.lendacky@....com>,
        "H. Peter Anvin" <hpa@...or.com>, Ard Biesheuvel <ardb@...nel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Jim Mattson <jmattson@...gle.com>,
        Andy Lutomirski <luto@...nel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Sergio Lopez <slp@...hat.com>, Peter Gonda <pgonda@...gle.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        David Rientjes <rientjes@...gle.com>,
        Dov Murik <dovmurik@...ux.ibm.com>,
        Tobin Feldman-Fitzthum <tobin@....com>,
        Michael Roth <michael.roth@....com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Andi Kleen <ak@...ux.intel.com>,
        "Dr . David Alan Gilbert" <dgilbert@...hat.com>,
        brijesh.ksingh@...il.com, tony.luck@...el.com, marcorr@...gle.com,
        sathyanarayanan.kuppuswamy@...ux.intel.com
Subject: Re: [PATCH v10 21/45] x86/mm: Add support to validate memory when
 changing C-bit



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
>>
>