RE: [tip: x86/mtrr] x86/hyperv: Set MTRR state when running as SEV-SNP Hyper-V guest

[Michael Kelley (LINUX)]

From: tip-bot2@xxxxxxxxxxxxx <tip-bot2@xxxxxxxxxxxxx> Sent: Monday, June 5, 2023 7:08 AM
> 
> The following commit has been merged into the x86/mtrr branch of tip:
> 
> Commit-ID:     c957f1f3c498bcce85c04e92e60afbae1fd10cde
> Gitweb:        https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git/commit/?id=c957f1f3c498bcce85c04e92e60afbae1fd10cde
> Author:        Juergen Gross <jgross@xxxxxxxx>
> AuthorDate:    Tue, 02 May 2023 14:09:19 +02:00
> Committer:     Borislav Petkov (AMD) <bp@xxxxxxxxx>
> CommitterDate: Thu, 01 Jun 2023 15:04:32 +02:00
> 
> x86/hyperv: Set MTRR state when running as SEV-SNP Hyper-V guest
> 
> 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 not supported by the hypervisor.
> 
> Fixes: 90b926e68f50 ("x86/pat: Fix pat_x_mtrr_type() for MTRR disabled case")
> Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
> Signed-off-by: Borislav Petkov (AMD) <bp@xxxxxxxxx>
> Tested-by: Michael Kelley <mikelley@xxxxxxxxxxxxx>
> Link: https://lore.kernel.org/all/20230502120931.20719-5-jgross@xxxxxxxx/
> Signed-off-by: Borislav Petkov (AMD) <bp@xxxxxxxxx>
> ---
>  arch/x86/hyperv/ivm.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/arch/x86/hyperv/ivm.c b/arch/x86/hyperv/ivm.c
> index cc92388..6f7c1b5 100644
> --- a/arch/x86/hyperv/ivm.c
> +++ b/arch/x86/hyperv/ivm.c
> @@ -17,6 +17,7 @@
>  #include <asm/mem_encrypt.h>
>  #include <asm/mshyperv.h>
>  #include <asm/hypervisor.h>
> +#include <asm/mtrr.h>
> 
>  #ifdef CONFIG_AMD_MEM_ENCRYPT
> 
> @@ -372,6 +373,9 @@ void __init hv_vtom_init(void)
>  	x86_platform.guest.enc_cache_flush_required = hv_vtom_cache_flush_required;
>  	x86_platform.guest.enc_tlb_flush_required = hv_vtom_tlb_flush_required;
>  	x86_platform.guest.enc_status_change_finish = hv_vtom_set_host_visibility;
> +
> +	/* Set WB as the default cache mode. */
> +	mtrr_overwrite_state(NULL, 0, MTRR_TYPE_WRBACK);
>  }
> 
>  #endif /* CONFIG_AMD_MEM_ENCRYPT */

FYI, I've tested SEV-SNP vTOM Hyper-V guests with linux-next20230607,
which includes all the MTRR changes.  Everything looks good.

Thanks!

Michael