[PATCH 1/2] x86/mm: Allow guest.enc_status_change_prepare() to fail

[PATCH 1/2] x86/mm: Allow guest.enc_status_change_prepare() to fail

[Kirill A. Shutemov]

TDX code is going to provide guest.enc_status_change_prepare() that is
able to fail.

Add a way to return an error from the callback.

While there, fix enc_status_change_finish_noop(). It is defined as
always-fail now which doesn't make sense for noop.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: stable@vger.kernel.org
---
 arch/x86/include/asm/x86_init.h | 2 +-
 arch/x86/kernel/x86_init.c      | 4 ++--
 arch/x86/mm/mem_encrypt_amd.c   | 4 +++-
 arch/x86/mm/pat/set_memory.c    | 3 ++-
 4 files changed, 8 insertions(+), 5 deletions(-)

diff --git a/arch/x86/include/asm/x86_init.h b/arch/x86/include/asm/x86_init.h
index 88085f369ff6..1ca9701917c5 100644
--- a/arch/x86/include/asm/x86_init.h
+++ b/arch/x86/include/asm/x86_init.h
@@ -150,7 +150,7 @@ struct x86_init_acpi {
  * @enc_cache_flush_required	Returns true if a cache flush is needed before changing page encryption status
  */
 struct x86_guest {
-	void (*enc_status_change_prepare)(unsigned long vaddr, int npages, bool enc);
+	bool (*enc_status_change_prepare)(unsigned long vaddr, int npages, bool enc);
 	bool (*enc_status_change_finish)(unsigned long vaddr, int npages, bool enc);
 	bool (*enc_tlb_flush_required)(bool enc);
 	bool (*enc_cache_flush_required)(void);
diff --git a/arch/x86/kernel/x86_init.c b/arch/x86/kernel/x86_init.c
index d82f4fa2f1bf..64664311ac2b 100644
--- a/arch/x86/kernel/x86_init.c
+++ b/arch/x86/kernel/x86_init.c
@@ -130,8 +130,8 @@ struct x86_cpuinit_ops x86_cpuinit = {
 
 static void default_nmi_init(void) { };
 
-static void enc_status_change_prepare_noop(unsigned long vaddr, int npages, bool enc) { }
-static bool enc_status_change_finish_noop(unsigned long vaddr, int npages, bool enc) { return false; }
+static bool enc_status_change_prepare_noop(unsigned long vaddr, int npages, bool enc) { return true; }
+static bool enc_status_change_finish_noop(unsigned long vaddr, int npages, bool enc) { return true; }
 static bool enc_tlb_flush_required_noop(bool enc) { return false; }
 static bool enc_cache_flush_required_noop(void) { return false; }
 static bool is_private_mmio_noop(u64 addr) {return false; }
diff --git a/arch/x86/mm/mem_encrypt_amd.c b/arch/x86/mm/mem_encrypt_amd.c
index e0b51c09109f..4f95c449a406 100644
--- a/arch/x86/mm/mem_encrypt_amd.c
+++ b/arch/x86/mm/mem_encrypt_amd.c
@@ -319,7 +319,7 @@ static void enc_dec_hypercall(unsigned long vaddr, int npages, bool enc)
 #endif
 }
 
-static void amd_enc_status_change_prepare(unsigned long vaddr, int npages, bool enc)
+static bool amd_enc_status_change_prepare(unsigned long vaddr, int npages, bool enc)
 {
 	/*
 	 * To maintain the security guarantees of SEV-SNP guests, make sure
@@ -327,6 +327,8 @@ static void amd_enc_status_change_prepare(unsigned long vaddr, int npages, bool
 	 */
 	if (cc_platform_has(CC_ATTR_GUEST_SEV_SNP) && !enc)
 		snp_set_memory_shared(vaddr, npages);
+
+	return true;
 }
 
 /* Return true unconditionally: return value doesn't matter for the SEV side */
diff --git a/arch/x86/mm/pat/set_memory.c b/arch/x86/mm/pat/set_memory.c
index 7159cf787613..b8f48ebe753c 100644
--- a/arch/x86/mm/pat/set_memory.c
+++ b/arch/x86/mm/pat/set_memory.c
@@ -2151,7 +2151,8 @@ static int __set_memory_enc_pgtable(unsigned long addr, int numpages, bool enc)
 		cpa_flush(&cpa, x86_platform.guest.enc_cache_flush_required());
 
 	/* Notify hypervisor that we are about to set/clr encryption attribute. */
-	x86_platform.guest.enc_status_change_prepare(addr, numpages, enc);
+	if (!x86_platform.guest.enc_status_change_prepare(addr, numpages, enc))
+		return -EIO;
 
 	ret = __change_page_attr_set_clr(&cpa, 1);
 
-- 
2.39.3

Re: [PATCH 1/2] x86/mm: Allow guest.enc_status_change_prepare() to fail

[Sathyanarayanan Kuppuswamy]

Hi,

On 5/25/23 3:58 PM, Kirill A. Shutemov wrote:
> TDX code is going to provide guest.enc_status_change_prepare() that is
> able to fail.

You can add some info about why you need this?

> 
> Add a way to return an error from the callback.
> 
> While there, fix enc_status_change_finish_noop(). It is defined as
> always-fail now which doesn't make sense for noop.

IMO, since the above change is an independent fix, I think it is better to
split this into a separate patch.

Other than above suggestions, the rest of the changes looks fine.

> 
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> Cc: stable@vger.kernel.org
> ---
>  arch/x86/include/asm/x86_init.h | 2 +-
>  arch/x86/kernel/x86_init.c      | 4 ++--
>  arch/x86/mm/mem_encrypt_amd.c   | 4 +++-
>  arch/x86/mm/pat/set_memory.c    | 3 ++-
>  4 files changed, 8 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/x86/include/asm/x86_init.h b/arch/x86/include/asm/x86_init.h
> index 88085f369ff6..1ca9701917c5 100644
> --- a/arch/x86/include/asm/x86_init.h
> +++ b/arch/x86/include/asm/x86_init.h
> @@ -150,7 +150,7 @@ struct x86_init_acpi {
>   * @enc_cache_flush_required	Returns true if a cache flush is needed before changing page encryption status
>   */
>  struct x86_guest {
> -	void (*enc_status_change_prepare)(unsigned long vaddr, int npages, bool enc);
> +	bool (*enc_status_change_prepare)(unsigned long vaddr, int npages, bool enc);
>  	bool (*enc_status_change_finish)(unsigned long vaddr, int npages, bool enc);
>  	bool (*enc_tlb_flush_required)(bool enc);
>  	bool (*enc_cache_flush_required)(void);
> diff --git a/arch/x86/kernel/x86_init.c b/arch/x86/kernel/x86_init.c
> index d82f4fa2f1bf..64664311ac2b 100644
> --- a/arch/x86/kernel/x86_init.c
> +++ b/arch/x86/kernel/x86_init.c
> @@ -130,8 +130,8 @@ struct x86_cpuinit_ops x86_cpuinit = {
>  
>  static void default_nmi_init(void) { };
>  
> -static void enc_status_change_prepare_noop(unsigned long vaddr, int npages, bool enc) { }
> -static bool enc_status_change_finish_noop(unsigned long vaddr, int npages, bool enc) { return false; }
> +static bool enc_status_change_prepare_noop(unsigned long vaddr, int npages, bool enc) { return true; }
> +static bool enc_status_change_finish_noop(unsigned long vaddr, int npages, bool enc) { return true; }
>  static bool enc_tlb_flush_required_noop(bool enc) { return false; }
>  static bool enc_cache_flush_required_noop(void) { return false; }
>  static bool is_private_mmio_noop(u64 addr) {return false; }
> diff --git a/arch/x86/mm/mem_encrypt_amd.c b/arch/x86/mm/mem_encrypt_amd.c
> index e0b51c09109f..4f95c449a406 100644
> --- a/arch/x86/mm/mem_encrypt_amd.c
> +++ b/arch/x86/mm/mem_encrypt_amd.c
> @@ -319,7 +319,7 @@ static void enc_dec_hypercall(unsigned long vaddr, int npages, bool enc)
>  #endif
>  }
>  
> -static void amd_enc_status_change_prepare(unsigned long vaddr, int npages, bool enc)
> +static bool amd_enc_status_change_prepare(unsigned long vaddr, int npages, bool enc)
>  {
>  	/*
>  	 * To maintain the security guarantees of SEV-SNP guests, make sure
> @@ -327,6 +327,8 @@ static void amd_enc_status_change_prepare(unsigned long vaddr, int npages, bool
>  	 */
>  	if (cc_platform_has(CC_ATTR_GUEST_SEV_SNP) && !enc)
>  		snp_set_memory_shared(vaddr, npages);
> +
> +	return true;
>  }
>  
>  /* Return true unconditionally: return value doesn't matter for the SEV side */
> diff --git a/arch/x86/mm/pat/set_memory.c b/arch/x86/mm/pat/set_memory.c
> index 7159cf787613..b8f48ebe753c 100644
> --- a/arch/x86/mm/pat/set_memory.c
> +++ b/arch/x86/mm/pat/set_memory.c
> @@ -2151,7 +2151,8 @@ static int __set_memory_enc_pgtable(unsigned long addr, int numpages, bool enc)
>  		cpa_flush(&cpa, x86_platform.guest.enc_cache_flush_required());
>  
>  	/* Notify hypervisor that we are about to set/clr encryption attribute. */
> -	x86_platform.guest.enc_status_change_prepare(addr, numpages, enc);
> +	if (!x86_platform.guest.enc_status_change_prepare(addr, numpages, enc))
> +		return -EIO;
>  
>  	ret = __change_page_attr_set_clr(&cpa, 1);
>  

-- 
Sathyanarayanan Kuppuswamy
Linux Kernel Developer

Re: [PATCH 1/2] x86/mm: Allow guest.enc_status_change_prepare() to fail

[Huang, Kai]

On Fri, 2023-05-26 at 01:58 +0300, Kirill A. Shutemov wrote:
> TDX code is going to provide guest.enc_status_change_prepare() that is
> able to fail.
> 
> Add a way to return an error from the callback.
> 
> While there, fix enc_status_change_finish_noop(). It is defined as
> always-fail now which doesn't make sense for noop.
> 
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> Cc: stable@vger.kernel.org
> ---
>  arch/x86/include/asm/x86_init.h | 2 +-
>  arch/x86/kernel/x86_init.c      | 4 ++--
>  arch/x86/mm/mem_encrypt_amd.c   | 4 +++-
>  arch/x86/mm/pat/set_memory.c    | 3 ++-
>  4 files changed, 8 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/x86/include/asm/x86_init.h b/arch/x86/include/asm/x86_init.h
> index 88085f369ff6..1ca9701917c5 100644
> --- a/arch/x86/include/asm/x86_init.h
> +++ b/arch/x86/include/asm/x86_init.h
> @@ -150,7 +150,7 @@ struct x86_init_acpi {
>   * @enc_cache_flush_required	Returns true if a cache flush is needed before changing page encryption status
>   */
>  struct x86_guest {
> -	void (*enc_status_change_prepare)(unsigned long vaddr, int npages, bool enc);
> +	bool (*enc_status_change_prepare)(unsigned long vaddr, int npages, bool enc);
> 

[...]

> @@ -2151,7 +2151,8 @@ static int __set_memory_enc_pgtable(unsigned long addr, int numpages, bool enc)
>  		cpa_flush(&cpa, x86_platform.guest.enc_cache_flush_required());
>  
>  	/* Notify hypervisor that we are about to set/clr encryption attribute. */
> -	x86_platform.guest.enc_status_change_prepare(addr, numpages, enc);
> +	if (!x86_platform.guest.enc_status_change_prepare(addr, numpages, enc))
> +		return -EIO;

The name "enc_status_change_prepare()" sounds like an action, but not some
true/false condition check.  I think it's more reasonable to make it return
'int', and returning 0 means successful?

Re: [PATCH 1/2] x86/mm: Allow guest.enc_status_change_prepare() to fail

[kirill.shutemov]

On Fri, May 26, 2023 at 02:17:12AM +0000, Huang, Kai wrote:
> On Fri, 2023-05-26 at 01:58 +0300, Kirill A. Shutemov wrote:
> > TDX code is going to provide guest.enc_status_change_prepare() that is
> > able to fail.
> > 
> > Add a way to return an error from the callback.
> > 
> > While there, fix enc_status_change_finish_noop(). It is defined as
> > always-fail now which doesn't make sense for noop.
> > 
> > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> > Cc: stable@vger.kernel.org
> > ---
> >  arch/x86/include/asm/x86_init.h | 2 +-
> >  arch/x86/kernel/x86_init.c      | 4 ++--
> >  arch/x86/mm/mem_encrypt_amd.c   | 4 +++-
> >  arch/x86/mm/pat/set_memory.c    | 3 ++-
> >  4 files changed, 8 insertions(+), 5 deletions(-)
> > 
> > diff --git a/arch/x86/include/asm/x86_init.h b/arch/x86/include/asm/x86_init.h
> > index 88085f369ff6..1ca9701917c5 100644
> > --- a/arch/x86/include/asm/x86_init.h
> > +++ b/arch/x86/include/asm/x86_init.h
> > @@ -150,7 +150,7 @@ struct x86_init_acpi {
> >   * @enc_cache_flush_required	Returns true if a cache flush is needed before changing page encryption status
> >   */
> >  struct x86_guest {
> > -	void (*enc_status_change_prepare)(unsigned long vaddr, int npages, bool enc);
> > +	bool (*enc_status_change_prepare)(unsigned long vaddr, int npages, bool enc);
> > 
> 
> [...]
> 
> > @@ -2151,7 +2151,8 @@ static int __set_memory_enc_pgtable(unsigned long addr, int numpages, bool enc)
> >  		cpa_flush(&cpa, x86_platform.guest.enc_cache_flush_required());
> >  
> >  	/* Notify hypervisor that we are about to set/clr encryption attribute. */
> > -	x86_platform.guest.enc_status_change_prepare(addr, numpages, enc);
> > +	if (!x86_platform.guest.enc_status_change_prepare(addr, numpages, enc))
> > +		return -EIO;
> 
> The name "enc_status_change_prepare()" sounds like an action, but not some
> true/false condition check.  I think it's more reasonable to make it return
> 'int', and returning 0 means successful?

It copies convention of enc_status_change_finish(). I don't think we need
anything more than binary pass/fail. We can change it in the future if
needed.

-- 
  Kiryl Shutsemau / Kirill A. Shutemov

[PATCH 2/2] x86/tdx: Fix race between set_memory_encrypted() and load_unaligned_zeropad()

[Kirill A. Shutemov]

Touching privately mapped GPA that is not properly converted to private
with MapGPA and accepted leads to unrecoverable exit to VMM.

load_unaligned_zeropad() can touch memory that is not owned by the
caller, but just happened to next after the owned memory.
This load_unaligned_zeropad() behaviour makes it important when kernel
asks VMM to convert a GPA from shared to private or back. Kernel must
never have a page mapped into direct mapping (and aliases) as private
when the GPA is already converted to shared or when GPA is not yet
converted to private.

guest.enc_status_change_prepare() called before adjusting direct mapping
and therefore it is responsible for converting the memory to private.

guest.enc_tlb_flush_required() called after adjusting direct mapping and
it converts the memory to shared.

It is okay to have a shared mapping of memory that is not converted
properly. handle_mmio() knows how to deal with load_unaligned_zeropad()
stepping on it.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Fixes: 7dbde7631629 ("x86/mm/cpa: Add support for TDX shared memory")
Cc: stable@vger.kernel.org
---
 arch/x86/coco/tdx/tdx.c | 56 ++++++++++++++++++++++++++++++++++++++---
 1 file changed, 53 insertions(+), 3 deletions(-)

diff --git a/arch/x86/coco/tdx/tdx.c b/arch/x86/coco/tdx/tdx.c
index e146b599260f..84525df750d4 100644
--- a/arch/x86/coco/tdx/tdx.c
+++ b/arch/x86/coco/tdx/tdx.c
@@ -840,6 +840,30 @@ static bool tdx_enc_status_changed(unsigned long vaddr, int numpages, bool enc)
 	return true;
 }
 
+static bool tdx_enc_status_change_prepare(unsigned long vaddr, int numpages,
+					  bool enc)
+{
+	/*
+	 * Only handle shared->private conversion here.
+	 * See the comment in tdx_early_init().
+	 */
+	if (enc)
+		return tdx_enc_status_changed(vaddr, numpages, enc);
+	return true;
+}
+
+static bool tdx_enc_status_change_finish(unsigned long vaddr, int numpages,
+					 bool enc)
+{
+	/*
+	 * Only handle private->shared conversion here.
+	 * See the comment in tdx_early_init().
+	 */
+	if (!enc)
+		return tdx_enc_status_changed(vaddr, numpages, enc);
+	return true;
+}
+
 void __init tdx_early_init(void)
 {
 	u64 cc_mask;
@@ -867,9 +891,35 @@ void __init tdx_early_init(void)
 	 */
 	physical_mask &= cc_mask - 1;
 
-	x86_platform.guest.enc_cache_flush_required = tdx_cache_flush_required;
-	x86_platform.guest.enc_tlb_flush_required   = tdx_tlb_flush_required;
-	x86_platform.guest.enc_status_change_finish = tdx_enc_status_changed;
+	/*
+	 * Touching privately mapped GPA that is not properly converted to
+	 * private with MapGPA and accepted leads to unrecoverable exit
+	 * to VMM.
+	 *
+	 * load_unaligned_zeropad() can touch memory that is not owned by
+	 * the caller, but just happened to next after the owned memory.
+	 * This load_unaligned_zeropad() behaviour makes it important when
+	 * kernel asks VMM to convert a GPA from shared to private or back.
+	 * Kernel must never have a page mapped into direct mapping (and
+	 * aliases) as private when the GPA is already converted to shared or
+	 * when GPA is not yet converted to private.
+	 *
+	 * guest.enc_status_change_prepare() called before adjusting direct
+	 * mapping and therefore it is responsible for converting the memory
+	 * to private.
+	 *
+	 * guest.enc_tlb_flush_required() called after adjusting direct mapping
+	 * and it converts the memory to shared.
+	 *
+	 * It is okay to have a shared mapping of memory that is not converted
+	 * properly. handle_mmio() knows how to deal with load_unaligned_zeropad()
+	 * stepping on it.
+	 */
+	x86_platform.guest.enc_status_change_prepare = tdx_enc_status_change_prepare;
+	x86_platform.guest.enc_status_change_finish  = tdx_enc_status_change_finish;
+
+	x86_platform.guest.enc_cache_flush_required  = tdx_cache_flush_required;
+	x86_platform.guest.enc_tlb_flush_required    = tdx_tlb_flush_required;
 
 	pr_info("Guest detected\n");
 }
-- 
2.39.3

Re: [PATCH 2/2] x86/tdx: Fix race between set_memory_encrypted() and load_unaligned_zeropad()

[Sathyanarayanan Kuppuswamy]

Hi, 

On 5/25/23 3:58 PM, Kirill A. Shutemov wrote:
> Touching privately mapped GPA that is not properly converted to private
> with MapGPA and accepted leads to unrecoverable exit to VMM.
> 
> load_unaligned_zeropad() can touch memory that is not owned by the
> caller, but just happened to next after the owned memory.
> This load_unaligned_zeropad() behaviour makes it important when kernel
> asks VMM to convert a GPA from shared to private or back. Kernel must
> never have a page mapped into direct mapping (and aliases) as private
> when the GPA is already converted to shared or when GPA is not yet
> converted to private.
> 
> guest.enc_status_change_prepare() called before adjusting direct mapping
> and therefore it is responsible for converting the memory to private.
> 
> guest.enc_tlb_flush_required() called after adjusting direct mapping and
> it converts the memory to shared.

Do you mean .enc_status_change_finish() here? Isn't enc_tlb_flush_required()
called before adjusting the mapping?

> 
> It is okay to have a shared mapping of memory that is not converted
> properly. handle_mmio() knows how to deal with load_unaligned_zeropad()
> stepping on it.
> 
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> Fixes: 7dbde7631629 ("x86/mm/cpa: Add support for TDX shared memory")
> Cc: stable@vger.kernel.org
> ---
>  arch/x86/coco/tdx/tdx.c | 56 ++++++++++++++++++++++++++++++++++++++---
>  1 file changed, 53 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/coco/tdx/tdx.c b/arch/x86/coco/tdx/tdx.c
> index e146b599260f..84525df750d4 100644
> --- a/arch/x86/coco/tdx/tdx.c
> +++ b/arch/x86/coco/tdx/tdx.c
> @@ -840,6 +840,30 @@ static bool tdx_enc_status_changed(unsigned long vaddr, int numpages, bool enc)
>  	return true;
>  }
>  
> +static bool tdx_enc_status_change_prepare(unsigned long vaddr, int numpages,
> +					  bool enc)
> +{
> +	/*
> +	 * Only handle shared->private conversion here.
> +	 * See the comment in tdx_early_init().
> +	 */
> +	if (enc)
> +		return tdx_enc_status_changed(vaddr, numpages, enc);
> +	return true;
> +}
> +
> +static bool tdx_enc_status_change_finish(unsigned long vaddr, int numpages,
> +					 bool enc)
> +{
> +	/*
> +	 * Only handle private->shared conversion here.
> +	 * See the comment in tdx_early_init().
> +	 */
> +	if (!enc)
> +		return tdx_enc_status_changed(vaddr, numpages, enc);
> +	return true;
> +}
> +
>  void __init tdx_early_init(void)
>  {
>  	u64 cc_mask;
> @@ -867,9 +891,35 @@ void __init tdx_early_init(void)
>  	 */
>  	physical_mask &= cc_mask - 1;
>  
> -	x86_platform.guest.enc_cache_flush_required = tdx_cache_flush_required;
> -	x86_platform.guest.enc_tlb_flush_required   = tdx_tlb_flush_required;
> -	x86_platform.guest.enc_status_change_finish = tdx_enc_status_changed;
> +	/*
> +	 * Touching privately mapped GPA that is not properly converted to
> +	 * private with MapGPA and accepted leads to unrecoverable exit
> +	 * to VMM.
> +	 *
> +	 * load_unaligned_zeropad() can touch memory that is not owned by
> +	 * the caller, but just happened to next after the owned memory.
> +	 * This load_unaligned_zeropad() behaviour makes it important when
> +	 * kernel asks VMM to convert a GPA from shared to private or back.
> +	 * Kernel must never have a page mapped into direct mapping (and
> +	 * aliases) as private when the GPA is already converted to shared or
> +	 * when GPA is not yet converted to private.
> +	 *
> +	 * guest.enc_status_change_prepare() called before adjusting direct
> +	 * mapping and therefore it is responsible for converting the memory
> +	 * to private.
> +	 *
> +	 * guest.enc_tlb_flush_required() called after adjusting direct mapping
> +	 * and it converts the memory to shared.

Same as above. Is it .enc_status_change_finish() here?

> +	 *
> +	 * It is okay to have a shared mapping of memory that is not converted
> +	 * properly. handle_mmio() knows how to deal with load_unaligned_zeropad()
> +	 * stepping on it.
> +	 */
> +	x86_platform.guest.enc_status_change_prepare = tdx_enc_status_change_prepare;
> +	x86_platform.guest.enc_status_change_finish  = tdx_enc_status_change_finish;
> +
> +	x86_platform.guest.enc_cache_flush_required  = tdx_cache_flush_required;
> +	x86_platform.guest.enc_tlb_flush_required    = tdx_tlb_flush_required;
>  
>  	pr_info("Guest detected\n");
>  }

-- 
Sathyanarayanan Kuppuswamy
Linux Kernel Developer

Re: [PATCH 2/2] x86/tdx: Fix race between set_memory_encrypted() and load_unaligned_zeropad()

[Kirill A. Shutemov]

On Thu, May 25, 2023 at 04:40:00PM -0700, Sathyanarayanan Kuppuswamy wrote:
> Hi, 
> 
> On 5/25/23 3:58 PM, Kirill A. Shutemov wrote:
> > Touching privately mapped GPA that is not properly converted to private
> > with MapGPA and accepted leads to unrecoverable exit to VMM.
> > 
> > load_unaligned_zeropad() can touch memory that is not owned by the
> > caller, but just happened to next after the owned memory.
> > This load_unaligned_zeropad() behaviour makes it important when kernel
> > asks VMM to convert a GPA from shared to private or back. Kernel must
> > never have a page mapped into direct mapping (and aliases) as private
> > when the GPA is already converted to shared or when GPA is not yet
> > converted to private.
> > 
> > guest.enc_status_change_prepare() called before adjusting direct mapping
> > and therefore it is responsible for converting the memory to private.
> > 
> > guest.enc_tlb_flush_required() called after adjusting direct mapping and
> > it converts the memory to shared.
> 
> Do you mean .enc_status_change_finish() here? Isn't enc_tlb_flush_required()
> called before adjusting the mapping?

Yes, I copy-pasted wrong callback :/

-- 
  Kiryl Shutsemau / Kirill A. Shutemov