Re: [PATCH v6 10/14] mm: x86: Invoke hypercall when page encryption status is changed

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

On Fri, Apr 03, 2020 at 02:07:02PM -0700, Krish Sadhukhan wrote:
> 
> On 3/29/20 11:22 PM, Ashish Kalra wrote:
> > From: Brijesh Singh <Brijesh.Singh@amd.com>
> > 
> > Invoke a hypercall when a memory region is changed from encrypted ->
> > decrypted and vice versa. Hypervisor need to know the page encryption
> > status during the guest migration.
> > 
> > Cc: Thomas Gleixner <tglx@linutronix.de>
> > Cc: Ingo Molnar <mingo@redhat.com>
> > Cc: "H. Peter Anvin" <hpa@zytor.com>
> > Cc: Paolo Bonzini <pbonzini@redhat.com>
> > Cc: "Radim Krčmář" <rkrcmar@redhat.com>
> > Cc: Joerg Roedel <joro@8bytes.org>
> > Cc: Borislav Petkov <bp@suse.de>
> > Cc: Tom Lendacky <thomas.lendacky@amd.com>
> > Cc: x86@kernel.org
> > Cc: kvm@vger.kernel.org
> > Cc: linux-kernel@vger.kernel.org
> > Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
> > Signed-off-by: Ashish Kalra <ashish.kalra@amd.com>
> > ---
> >   arch/x86/include/asm/paravirt.h       | 10 +++++
> >   arch/x86/include/asm/paravirt_types.h |  2 +
> >   arch/x86/kernel/paravirt.c            |  1 +
> >   arch/x86/mm/mem_encrypt.c             | 57 ++++++++++++++++++++++++++-
> >   arch/x86/mm/pat/set_memory.c          |  7 ++++
> >   5 files changed, 76 insertions(+), 1 deletion(-)
> > 
> > diff --git a/arch/x86/include/asm/paravirt.h b/arch/x86/include/asm/paravirt.h
> > index 694d8daf4983..8127b9c141bf 100644
> > --- a/arch/x86/include/asm/paravirt.h
> > +++ b/arch/x86/include/asm/paravirt.h
> > @@ -78,6 +78,12 @@ static inline void paravirt_arch_exit_mmap(struct mm_struct *mm)
> >   	PVOP_VCALL1(mmu.exit_mmap, mm);
> >   }
> > +static inline void page_encryption_changed(unsigned long vaddr, int npages,
> > +						bool enc)
> > +{
> > +	PVOP_VCALL3(mmu.page_encryption_changed, vaddr, npages, enc);
> > +}
> > +
> >   #ifdef CONFIG_PARAVIRT_XXL
> >   static inline void load_sp0(unsigned long sp0)
> >   {
> > @@ -946,6 +952,10 @@ static inline void paravirt_arch_dup_mmap(struct mm_struct *oldmm,
> >   static inline void paravirt_arch_exit_mmap(struct mm_struct *mm)
> >   {
> >   }
> > +
> > +static inline void page_encryption_changed(unsigned long vaddr, int npages, bool enc)
> > +{
> > +}
> >   #endif
> >   #endif /* __ASSEMBLY__ */
> >   #endif /* _ASM_X86_PARAVIRT_H */
> > diff --git a/arch/x86/include/asm/paravirt_types.h b/arch/x86/include/asm/paravirt_types.h
> > index 732f62e04ddb..03bfd515c59c 100644
> > --- a/arch/x86/include/asm/paravirt_types.h
> > +++ b/arch/x86/include/asm/paravirt_types.h
> > @@ -215,6 +215,8 @@ struct pv_mmu_ops {
> >   	/* Hook for intercepting the destruction of an mm_struct. */
> >   	void (*exit_mmap)(struct mm_struct *mm);
> > +	void (*page_encryption_changed)(unsigned long vaddr, int npages,
> > +					bool enc);
> >   #ifdef CONFIG_PARAVIRT_XXL
> >   	struct paravirt_callee_save read_cr2;
> > diff --git a/arch/x86/kernel/paravirt.c b/arch/x86/kernel/paravirt.c
> > index c131ba4e70ef..840c02b23aeb 100644
> > --- a/arch/x86/kernel/paravirt.c
> > +++ b/arch/x86/kernel/paravirt.c
> > @@ -367,6 +367,7 @@ struct paravirt_patch_template pv_ops = {
> >   			(void (*)(struct mmu_gather *, void *))tlb_remove_page,
> >   	.mmu.exit_mmap		= paravirt_nop,
> > +	.mmu.page_encryption_changed	= paravirt_nop,
> >   #ifdef CONFIG_PARAVIRT_XXL
> >   	.mmu.read_cr2		= __PV_IS_CALLEE_SAVE(native_read_cr2),
> > diff --git a/arch/x86/mm/mem_encrypt.c b/arch/x86/mm/mem_encrypt.c
> > index f4bd4b431ba1..c9800fa811f6 100644
> > --- a/arch/x86/mm/mem_encrypt.c
> > +++ b/arch/x86/mm/mem_encrypt.c
> > @@ -19,6 +19,7 @@
> >   #include <linux/kernel.h>
> >   #include <linux/bitops.h>
> >   #include <linux/dma-mapping.h>
> > +#include <linux/kvm_para.h>
> >   #include <asm/tlbflush.h>
> >   #include <asm/fixmap.h>
> > @@ -29,6 +30,7 @@
> >   #include <asm/processor-flags.h>
> >   #include <asm/msr.h>
> >   #include <asm/cmdline.h>
> > +#include <asm/kvm_para.h>
> >   #include "mm_internal.h"
> > @@ -196,6 +198,47 @@ void __init sme_early_init(void)
> >   		swiotlb_force = SWIOTLB_FORCE;
> >   }
> > +static void set_memory_enc_dec_hypercall(unsigned long vaddr, int npages,
> > +					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;
> > +		}
> 
> 
> Is it possible to re-use the code in __set_clr_pte_enc() ?
> 
> > +
> > +		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;
> > +	}
> > +}
> > +
> >   static void __init __set_clr_pte_enc(pte_t *kpte, int level, bool enc)
> >   {
> >   	pgprot_t old_prot, new_prot;
> > @@ -253,12 +296,13 @@ 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;
> > @@ -313,6 +357,8 @@ 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);
> 
> 
> If I haven't missed anything, it seems early_set_memory_encrypted() doesn't
> have a caller. So is there a possibility that we can end up calling it in
> non-SEV context and hence do we need to have the sev_active() guard here ?
> 

As of now early_set_memory_encrypted() is not used, but
early_set_memory_decrypted() is used in __set_percpu_decrypted() and
that is called with the sev_active() check.

Thanks,
Ashish

> >   out:
> >   	__flush_tlb_all();
> >   	return ret;
> > @@ -451,6 +497,15 @@ void __init mem_encrypt_init(void)
> >   	if (sev_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
> > +
> >   	pr_info("AMD %s active\n",
> >   		sev_active() ? "Secure Encrypted Virtualization (SEV)"
> >   			     : "Secure Memory Encryption (SME)");
> > diff --git a/arch/x86/mm/pat/set_memory.c b/arch/x86/mm/pat/set_memory.c
> > index c4aedd00c1ba..86b7804129fc 100644
> > --- a/arch/x86/mm/pat/set_memory.c
> > +++ b/arch/x86/mm/pat/set_memory.c
> > @@ -26,6 +26,7 @@
> >   #include <asm/proto.h>
> >   #include <asm/memtype.h>
> >   #include <asm/set_memory.h>
> > +#include <asm/paravirt.h>
> >   #include "../mm_internal.h"
> > @@ -1987,6 +1988,12 @@ 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.
> > +	 */
> > +	page_encryption_changed(addr, numpages, enc);
> > +
> >   	return ret;
> >   }