diff mbox series

[v3,02/14] x86/ioapic: Gate decrypted mapping on cc_platform_has() attribute

Message ID 1668624097-14884-3-git-send-email-mikelley@microsoft.com
State New
Headers
Series Add PCI pass-thru support to Hyper-V Confidential VMs |

Commit Message

Michael Kelley (LINUX) Nov. 16, 2022, 6:41 p.m. UTC 
  Current code always maps the IOAPIC as shared (decrypted) in a
confidential VM. But Hyper-V guest VMs on AMD SEV-SNP with vTOM
enabled use a paravisor running in VMPL0 to emulate the IOAPIC.
In such a case, the IOAPIC must be accessed as private (encrypted).

Fix this by gating the IOAPIC decrypted mapping on a new
cc_platform_has() attribute that a subsequent patch in the series
will set only for Hyper-V guests.

Signed-off-by: Michael Kelley <mikelley@microsoft.com>
Reviewed-by: Wei Liu <wei.liu@kernel.org>
---
 arch/x86/kernel/apic/io_apic.c |  3 ++-
 include/linux/cc_platform.h    | 12 ++++++++++++
 2 files changed, 14 insertions(+), 1 deletion(-)

Comments

Kuppuswamy Sathyanarayanan Nov. 17, 2022, 9:39 p.m. UTC | #1 
On 11/16/22 10:41 AM, Michael Kelley wrote:
> Current code always maps the IOAPIC as shared (decrypted) in a
> confidential VM. But Hyper-V guest VMs on AMD SEV-SNP with vTOM
> enabled use a paravisor running in VMPL0 to emulate the IOAPIC.
> In such a case, the IOAPIC must be accessed as private (encrypted).
> 
> Fix this by gating the IOAPIC decrypted mapping on a new
> cc_platform_has() attribute that a subsequent patch in the series
> will set only for Hyper-V guests.
> 
> Signed-off-by: Michael Kelley <mikelley@microsoft.com>
> Reviewed-by: Wei Liu <wei.liu@kernel.org>
> ---

Looks fine to me.

Reviewed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>

>  arch/x86/kernel/apic/io_apic.c |  3 ++-
>  include/linux/cc_platform.h    | 12 ++++++++++++
>  2 files changed, 14 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kernel/apic/io_apic.c b/arch/x86/kernel/apic/io_apic.c
> index a868b76..c65e0cc 100644
> --- a/arch/x86/kernel/apic/io_apic.c
> +++ b/arch/x86/kernel/apic/io_apic.c
> @@ -2686,7 +2686,8 @@ static void io_apic_set_fixmap(enum fixed_addresses idx, phys_addr_t phys)
>  	 * Ensure fixmaps for IOAPIC MMIO respect memory encryption pgprot
>  	 * bits, just like normal ioremap():
>  	 */
> -	flags = pgprot_decrypted(flags);
> +	if (!cc_platform_has(CC_ATTR_EMULATED_IOAPIC))
> +		flags = pgprot_decrypted(flags);
>  
>  	__set_fixmap(idx, phys, flags);
>  }
> diff --git a/include/linux/cc_platform.h b/include/linux/cc_platform.h
> index cb0d6cd..7a0da75 100644
> --- a/include/linux/cc_platform.h
> +++ b/include/linux/cc_platform.h
> @@ -90,6 +90,18 @@ enum cc_attr {
>  	 * Examples include TDX Guest.
>  	 */
>  	CC_ATTR_HOTPLUG_DISABLED,
> +
> +	/**
> +	 * @CC_ATTR_EMULATED_IOAPIC: Guest VM has an emulated I/O APIC
> +	 *
> +	 * The platform/OS is running as a guest/virtual machine with
> +	 * an I/O APIC that is emulated by a paravisor running in the
> +	 * guest VM context. As such, the I/O APIC is accessed in the
> +	 * encrypted portion of the guest physical address space.
> +	 *
> +	 * Examples include Hyper-V SEV-SNP guests using vTOM.
> +	 */
> +	CC_ATTR_EMULATED_IOAPIC,
>  };
>  
>  #ifdef CONFIG_ARCH_HAS_CC_PLATFORM
Borislav Petkov Nov. 21, 2022, 1:50 p.m. UTC | #2 
On Wed, Nov 16, 2022 at 10:41:25AM -0800, Michael Kelley wrote:
> Current code always maps the IOAPIC as shared (decrypted) in a
> confidential VM. But Hyper-V guest VMs on AMD SEV-SNP with vTOM
> enabled use a paravisor running in VMPL0 to emulate the IOAPIC.

"IO-APIC" I guess, in all your text.

> In such a case, the IOAPIC must be accessed as private (encrypted).

So the condition for the IO-APIC is pretty specific but the naming
CC_ATTR_EMULATED_IOAPIC too generic. Other HVs emulate IO-APICs too,
right?

If you have to be precise, the proper check should be (pseudo code):

 if (cc_vendor(HYPERV) &&
     SNP enabled &&
     SNP features has vTOM &&
     paravisor in use)

so I guess you're probably better off calling it

  CC_ATTR_ACCESS_IOAPIC_ENCRYPTED

which then gets set on exactly those guests and nothing else.

I'd say.

Thx.
Michael Kelley (LINUX) Nov. 21, 2022, 4:43 p.m. UTC | #3 
From: Borislav Petkov <bp@alien8.de> Sent: Monday, November 21, 2022 5:51 AM
> 
> On Wed, Nov 16, 2022 at 10:41:25AM -0800, Michael Kelley wrote:
> > Current code always maps the IOAPIC as shared (decrypted) in a
> > confidential VM. But Hyper-V guest VMs on AMD SEV-SNP with vTOM
> > enabled use a paravisor running in VMPL0 to emulate the IOAPIC.
> 
> "IO-APIC" I guess, in all your text.
> 
> > In such a case, the IOAPIC must be accessed as private (encrypted).
> 
> So the condition for the IO-APIC is pretty specific but the naming
> CC_ATTR_EMULATED_IOAPIC too generic. Other HVs emulate IO-APICs too,
> right?
> 
> If you have to be precise, the proper check should be (pseudo code):
> 
>  if (cc_vendor(HYPERV) &&
>      SNP enabled &&
>      SNP features has vTOM &&
>      paravisor in use)
> 
> so I guess you're probably better off calling it
> 
>   CC_ATTR_ACCESS_IOAPIC_ENCRYPTED
> 
> which then gets set on exactly those guests and nothing else.
> 
> I'd say.
> 

I'm OK with naming it very narrowly.  When/if there's a more general
case later, we can generalize to whatever degree is appropriate.

Michael
Borislav Petkov Nov. 21, 2022, 7:47 p.m. UTC | #4 
On Mon, Nov 21, 2022 at 04:43:01PM +0000, Michael Kelley (LINUX) wrote:
> I'm OK with naming it very narrowly.  When/if there's a more general
> case later, we can generalize to whatever degree is appropriate.

Exactly.

Those defines are free to change when we see fit.
diff mbox series

Patch

diff --git a/arch/x86/kernel/apic/io_apic.c b/arch/x86/kernel/apic/io_apic.c
index a868b76..c65e0cc 100644
--- a/arch/x86/kernel/apic/io_apic.c
+++ b/arch/x86/kernel/apic/io_apic.c
@@ -2686,7 +2686,8 @@  static void io_apic_set_fixmap(enum fixed_addresses idx, phys_addr_t phys)
 	 * Ensure fixmaps for IOAPIC MMIO respect memory encryption pgprot
 	 * bits, just like normal ioremap():
 	 */
-	flags = pgprot_decrypted(flags);
+	if (!cc_platform_has(CC_ATTR_EMULATED_IOAPIC))
+		flags = pgprot_decrypted(flags);
 
 	__set_fixmap(idx, phys, flags);
 }
diff --git a/include/linux/cc_platform.h b/include/linux/cc_platform.h
index cb0d6cd..7a0da75 100644
--- a/include/linux/cc_platform.h
+++ b/include/linux/cc_platform.h
@@ -90,6 +90,18 @@  enum cc_attr {
 	 * Examples include TDX Guest.
 	 */
 	CC_ATTR_HOTPLUG_DISABLED,
+
+	/**
+	 * @CC_ATTR_EMULATED_IOAPIC: Guest VM has an emulated I/O APIC
+	 *
+	 * The platform/OS is running as a guest/virtual machine with
+	 * an I/O APIC that is emulated by a paravisor running in the
+	 * guest VM context. As such, the I/O APIC is accessed in the
+	 * encrypted portion of the guest physical address space.
+	 *
+	 * Examples include Hyper-V SEV-SNP guests using vTOM.
+	 */
+	CC_ATTR_EMULATED_IOAPIC,
 };
 
 #ifdef CONFIG_ARCH_HAS_CC_PLATFORM