linux-kernel - Re: [PATCH v13 09/12] mm: x86: Invoke hypercall when page encryption status is changed

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Message-ID: <f63735b4-8ec2-fdb4-0bac-8ee0921268b0@redhat.com>
Date:   Wed, 21 Apr 2021 14:00:42 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Borislav Petkov <bp@...en8.de>, Ashish Kalra <Ashish.Kalra@....com>
Cc:     tglx@...utronix.de, mingo@...hat.com, hpa@...or.com,
        joro@...tes.org, thomas.lendacky@....com, x86@...nel.org,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        srutherford@...gle.com, seanjc@...gle.com,
        venu.busireddy@...cle.com, brijesh.singh@....com
Subject: Re: [PATCH v13 09/12] mm: x86: Invoke hypercall when page encryption
 status is changed

On 21/04/21 12:05, Borislav Petkov wrote:
> On Thu, Apr 15, 2021 at 03:57:26PM +0000, Ashish Kalra wrote:
>> +static inline void page_encryption_changed(unsigned long vaddr, int npages,
>> +						bool enc)
> 
> When you see a function name "page_encryption_changed", what does that
> tell you about what that function does?
> 
> Dunno but it doesn't tell me a whole lot.
> 
> Now look at the other function names in struct pv_mmu_ops.
> 
> See the difference?
> 
>> +static void set_memory_enc_dec_hypercall(unsigned long vaddr, int npages,
> 
> If I had to guess what that function does just by reading its name, it
> sets a memory encryption/decryption hypercall.
> 
> Am I close?

The words are right but the order is wrong (more like "hypercall to set 
some memory's encrypted/decrypted state").  Perhaps? 
kvm_hypercall_set_page_enc_status.

page_encryption_changed does not sound bad to me though, it's a 
notification-like function name.  Maybe notify_page_enc_status_changed?

Paolo

>> +					bool enc)
>> +{
>> +	unsigned long sz = npages << PAGE_SHIFT;
>> +	unsigned long vaddr_end, vaddr_next;
>> +
>> +	vaddr_end = vaddr + sz;
>> +
>> +	for (; vaddr < vaddr_end; vaddr = vaddr_next) {
>> +		int psize, pmask, level;
>> +		unsigned long pfn;
>> +		pte_t *kpte;
>> +
>> +		kpte = lookup_address(vaddr, &level);
>> +		if (!kpte || pte_none(*kpte))
>> +			return;
>> +
>> +		switch (level) {
>> +		case PG_LEVEL_4K:
>> +			pfn = pte_pfn(*kpte);
>> +			break;
>> +		case PG_LEVEL_2M:
>> +			pfn = pmd_pfn(*(pmd_t *)kpte);
>> +			break;
>> +		case PG_LEVEL_1G:
>> +			pfn = pud_pfn(*(pud_t *)kpte);
>> +			break;
>> +		default:
>> +			return;
>> +		}
> 
> Pretty much that same thing is in __set_clr_pte_enc(). Make a helper
> function pls.
> 
>> +
>> +		psize = page_level_size(level);
>> +		pmask = page_level_mask(level);
>> +
>> +		kvm_sev_hypercall3(KVM_HC_PAGE_ENC_STATUS,
>> +				   pfn << PAGE_SHIFT, psize >> PAGE_SHIFT, enc);
>> +
>> +		vaddr_next = (vaddr & pmask) + psize;
>> +	}
> 
> As with other patches from Brijesh, that should be a while loop. :)
> 
>> +}
>> +
>>   static void __init __set_clr_pte_enc(pte_t *kpte, int level, bool enc)
>>   {
>>   	pgprot_t old_prot, new_prot;
>> @@ -286,12 +329,13 @@ static void __init __set_clr_pte_enc(pte_t *kpte, int level, bool enc)
>>   static int __init early_set_memory_enc_dec(unsigned long vaddr,
>>   					   unsigned long size, bool enc)
>>   {
>> -	unsigned long vaddr_end, vaddr_next;
>> +	unsigned long vaddr_end, vaddr_next, start;
>>   	unsigned long psize, pmask;
>>   	int split_page_size_mask;
>>   	int level, ret;
>>   	pte_t *kpte;
>>   
>> +	start = vaddr;
>>   	vaddr_next = vaddr;
>>   	vaddr_end = vaddr + size;
>>   
>> @@ -346,6 +390,8 @@ static int __init early_set_memory_enc_dec(unsigned long vaddr,
>>   
>>   	ret = 0;
>>   
>> +	set_memory_enc_dec_hypercall(start, PAGE_ALIGN(size) >> PAGE_SHIFT,
>> +					enc);
>>   out:
>>   	__flush_tlb_all();
>>   	return ret;
>> @@ -481,6 +527,15 @@ void __init mem_encrypt_init(void)
>>   	if (sev_active() && !sev_es_active())
>>   		static_branch_enable(&sev_enable_key);
>>   
>> +#ifdef CONFIG_PARAVIRT
>> +	/*
>> +	 * With SEV, we need to make a hypercall when page encryption state is
>> +	 * changed.
>> +	 */
>> +	if (sev_active())
>> +		pv_ops.mmu.page_encryption_changed = set_memory_enc_dec_hypercall;
>> +#endif
> 
> There's already a sev_active() check above it. Merge the two pls.
> 
>> +
>>   	print_mem_encrypt_feature_info();
>>   }
>>   
>> diff --git a/arch/x86/mm/pat/set_memory.c b/arch/x86/mm/pat/set_memory.c
>> index 16f878c26667..3576b583ac65 100644
>> --- a/arch/x86/mm/pat/set_memory.c
>> +++ b/arch/x86/mm/pat/set_memory.c
>> @@ -27,6 +27,7 @@
>>   #include <asm/proto.h>
>>   #include <asm/memtype.h>
>>   #include <asm/set_memory.h>
>> +#include <asm/paravirt.h>
>>   
>>   #include "../mm_internal.h"
>>   
>> @@ -2012,6 +2013,12 @@ static int __set_memory_enc_dec(unsigned long addr, int numpages, bool enc)
>>   	 */
>>   	cpa_flush(&cpa, 0);
>>   
>> +	/* Notify hypervisor that a given memory range is mapped encrypted
>> +	 * or decrypted. The hypervisor will use this information during the
>> +	 * VM migration.
>> +	 */
> 
> Kernel comments style is:
> 
> 	/*
> 	 * A sentence ending with a full-stop.
> 	 * Another sentence. ...
> 	 * More sentences. ...
> 	 */
>