linux-kernel - Re: [Part1 PATCH v4 16/17] X86/KVM: Unencrypt shared per-cpu variables when SEV is active

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Date:   Tue, 19 Sep 2017 09:00:39 -0500
From:   Brijesh Singh <brijesh.singh@....com>
To:     Borislav Petkov <bp@...e.de>
Cc:     brijesh.singh@....com, linux-kernel@...r.kernel.org,
        x86@...nel.org, kvm@...r.kernel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H . Peter Anvin" <hpa@...or.com>,
        Andy Lutomirski <luto@...nel.org>,
        Tom Lendacky <thomas.lendacky@....com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>
Subject: Re: [Part1 PATCH v4 16/17] X86/KVM: Unencrypt shared per-cpu
 variables when SEV is active



On 09/19/2017 06:06 AM, Borislav Petkov wrote:
...

>> +	unsigned long pa = slow_virt_to_phys(var);
>> +
>> +	/* decrypt the memory in-place */
>> +	sme_early_decrypt(pa, size);
>> +
>> +	/* clear the C-bit from the page table */
>> +	early_set_memory_decrypted(pa, size);
> 
> So those two do a lot of work like TLB flushing and WBINVD for each
> per-CPU variable and normally I'd say you do this on one go instead of
> variable per variable and thus save yourself the subsequent expensive
> invalidation calls but we do it once only during boot so maybe something
> to think about later, when there's more time and boredom.
> 
> :)


Yes, we can revisit it later to optimize it.

...

> 
> Let it stick out and shorten function name:
> 
> 	for_each_possible_cpu(cpu) {
>                  __set_percpu_decrypted(&per_cpu(apf_reason, cpu),   sizeof(struct kvm_vcpu_pv_apf_data));
>                  __set_percpu_decrypted(&per_cpu(steal_time, cpu),   sizeof(struct kvm_steal_time));
>                  __set_percpu_decrypted(&per_cpu(kvm_apic_eoi, cpu), sizeof(unsigned long));
>          }
> 
> Also, we agreed to call everything that's not encrypted "decrypted" so
> that we have only two different states: encrypted and decrypted and thus
> less confusion.


Will do.