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

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Message-Id: <20230209072220.6836-4-jgross@suse.com>
Date:   Thu,  9 Feb 2023 08:22:15 +0100
From:   Juergen Gross <jgross@...e.com>
To:     linux-kernel@...r.kernel.org, x86@...nel.org,
        linux-hyperv@...r.kernel.org
Cc:     lists@...dbynature.de, mikelley@...rosoft.com,
        torvalds@...ux-foundation.org, Juergen Gross <jgross@...e.com>,
        "K. Y. Srinivasan" <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Wei Liu <wei.liu@...nel.org>, Dexuan Cui <decui@...rosoft.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>
Subject: [PATCH v2 3/8] 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 disabled by the hypervisor.

Fixes: 90b926e68f50 ("x86/pat: Fix pat_x_mtrr_type() for MTRR disabled case")
Signed-off-by: Juergen Gross <jgross@...e.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
+#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: */
-- 
2.35.3