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

[tip-bot2 for Juergen Gross]

The following commit has been merged into the x86/mtrr branch of tip:

Commit-ID:     c957f1f3c498bcce85c04e92e60afbae1fd10cde
Gitweb:        https://git.kernel.org/tip/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/r/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 */