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

[Ashish Kalra <ashish.kalra@amd.com>]

On Wed, Apr 21, 2021 at 12:05:08PM +0200, 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?
> 
> > +					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.
> 

Yes, both have some common code, but it is only this page level/size
check, and they pretty much do different things with page size
evaluation, i think it will be cleaner to keep the code separately for
both these functions.

> > +
> > +		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. :)
>

I see that early_set_memory_enc_dec() is also using a for loop, so which
patches are you referring to ?

> > +}
> > +
> >  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.
>

Ok. 

> > +
> >  	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. ...
> 	 */

Ok.

> 
> -- 
> Regards/Gruss,
>     Boris.
> 
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