diff mbox series

[v2,3/8] x86/hyperv: set MTRR state when running as SEV-SNP Hyper-V guest

Message ID 20230209072220.6836-4-jgross@suse.com
State New
Headers
Series x86/mtrr: fix handling with PAT but without MTRR |

Commit Message

Juergen Gross Feb. 9, 2023, 7:22 a.m. UTC 
  In order to avoid mappings using the UC- cache attribute, set the
MTRR state to use WB caching as the default.

This is needed in order to cope with the fact that PAT is enabled,
while MTRRs are disabled by the hypervisor.

Fixes: 90b926e68f50 ("x86/pat: Fix pat_x_mtrr_type() for MTRR disabled case")
Signed-off-by: Juergen Gross <jgross@suse.com>
---
V2:
- new patch
---
 arch/x86/kernel/cpu/mshyperv.c | 8 ++++++++
 1 file changed, 8 insertions(+)

Comments

Michael Kelley (LINUX) Feb. 13, 2023, 1:07 a.m. UTC | #1 
From: Juergen Gross <jgross@suse.com> Sent: Wednesday, February 8, 2023 11:22 PM
> 
> In order to avoid mappings using the UC- cache attribute, set the
> MTRR state to use WB caching as the default.
> 
> This is needed in order to cope with the fact that PAT is enabled,
> while MTRRs are disabled by the hypervisor.
> 
> Fixes: 90b926e68f50 ("x86/pat: Fix pat_x_mtrr_type() for MTRR disabled case")
> Signed-off-by: Juergen Gross <jgross@suse.com>
> ---
> V2:
> - new patch
> ---
>  arch/x86/kernel/cpu/mshyperv.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/arch/x86/kernel/cpu/mshyperv.c b/arch/x86/kernel/cpu/mshyperv.c
> index 46668e255421..51e47dc0e987 100644
> --- a/arch/x86/kernel/cpu/mshyperv.c
> +++ b/arch/x86/kernel/cpu/mshyperv.c
> @@ -34,6 +34,7 @@
>  #include <clocksource/hyperv_timer.h>
>  #include <asm/numa.h>
>  #include <asm/coco.h>
> +#include <asm/mtrr.h>
> 
>  /* Is Linux running as the root partition? */
>  bool hv_root_partition;
> @@ -335,6 +336,13 @@ static void __init ms_hyperv_init_platform(void)
>  			static_branch_enable(&isolation_type_snp);
>  #ifdef CONFIG_SWIOTLB
>  			swiotlb_unencrypted_base = ms_hyperv.shared_gpa_boundary;
> +#endif

Unfortunately, Hyper-V does not filter out the MTRR flag from the
CPUID leaf, so this code also needs 

			setup_clear_cpu_cap(X86_FEATURE_MTRR);

before calling mtrr_overwrite_state().  I've got a bug filed for the
Hyper-V team to fix the flag, but clearing the feature here solves the
problem regardless.

> +#ifdef CONFIG_MTRR

Hopefully this #ifdef can go away, per my comment in Patch 2 of
the series.

Michael

> +			/*
> +			 * Set WB as the default cache mode in case MTRRs are
> +			 * disabled by the hypervisor.
> +			 */
> +			mtrr_overwrite_state(NULL, 0, NULL, MTRR_TYPE_WRBACK);
>  #endif
>  		}
>  		/* Isolation VMs are unenlightened SEV-based VMs, thus this check: */
> --
> 2.35.3
Juergen Gross Feb. 13, 2023, 6:28 a.m. UTC | #2 
On 13.02.23 02:07, Michael Kelley (LINUX) wrote:
> From: Juergen Gross <jgross@suse.com> Sent: Wednesday, February 8, 2023 11:22 PM
>>
>> In order to avoid mappings using the UC- cache attribute, set the
>> MTRR state to use WB caching as the default.
>>
>> This is needed in order to cope with the fact that PAT is enabled,
>> while MTRRs are disabled by the hypervisor.
>>
>> Fixes: 90b926e68f50 ("x86/pat: Fix pat_x_mtrr_type() for MTRR disabled case")
>> Signed-off-by: Juergen Gross <jgross@suse.com>
>> ---
>> V2:
>> - new patch
>> ---
>>   arch/x86/kernel/cpu/mshyperv.c | 8 ++++++++
>>   1 file changed, 8 insertions(+)
>>
>> diff --git a/arch/x86/kernel/cpu/mshyperv.c b/arch/x86/kernel/cpu/mshyperv.c
>> index 46668e255421..51e47dc0e987 100644
>> --- a/arch/x86/kernel/cpu/mshyperv.c
>> +++ b/arch/x86/kernel/cpu/mshyperv.c
>> @@ -34,6 +34,7 @@
>>   #include <clocksource/hyperv_timer.h>
>>   #include <asm/numa.h>
>>   #include <asm/coco.h>
>> +#include <asm/mtrr.h>
>>
>>   /* Is Linux running as the root partition? */
>>   bool hv_root_partition;
>> @@ -335,6 +336,13 @@ static void __init ms_hyperv_init_platform(void)
>>   			static_branch_enable(&isolation_type_snp);
>>   #ifdef CONFIG_SWIOTLB
>>   			swiotlb_unencrypted_base = ms_hyperv.shared_gpa_boundary;
>> +#endif
> 
> Unfortunately, Hyper-V does not filter out the MTRR flag from the
> CPUID leaf, so this code also needs
> 
> 			setup_clear_cpu_cap(X86_FEATURE_MTRR);
> 
> before calling mtrr_overwrite_state().  I've got a bug filed for the
> Hyper-V team to fix the flag, but clearing the feature here solves the
> problem regardless.

Okay, will add it.

> 
>> +#ifdef CONFIG_MTRR
> 
> Hopefully this #ifdef can go away, per my comment in Patch 2 of
> the series.

As said already, fine with me.


Juergen
diff mbox series

Patch

diff --git a/arch/x86/kernel/cpu/mshyperv.c b/arch/x86/kernel/cpu/mshyperv.c
index 46668e255421..51e47dc0e987 100644
--- a/arch/x86/kernel/cpu/mshyperv.c
+++ b/arch/x86/kernel/cpu/mshyperv.c
@@ -34,6 +34,7 @@ 
 #include <clocksource/hyperv_timer.h>
 #include <asm/numa.h>
 #include <asm/coco.h>
+#include <asm/mtrr.h>
 
 /* Is Linux running as the root partition? */
 bool hv_root_partition;
@@ -335,6 +336,13 @@  static void __init ms_hyperv_init_platform(void)
 			static_branch_enable(&isolation_type_snp);
 #ifdef CONFIG_SWIOTLB
 			swiotlb_unencrypted_base = ms_hyperv.shared_gpa_boundary;
+#endif
+#ifdef CONFIG_MTRR
+			/*
+			 * Set WB as the default cache mode in case MTRRs are
+			 * disabled by the hypervisor.
+			 */
+			mtrr_overwrite_state(NULL, 0, NULL, MTRR_TYPE_WRBACK);
 #endif
 		}
 		/* Isolation VMs are unenlightened SEV-based VMs, thus this check: */