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

Ashish Kalra
2021-04-21T12:12:23Z

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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