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

Paolo Bonzini
2021-04-21T12:00:53Z

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. ...
> */
>