On Tue, Oct 15, 2024 at 12:12:51PM +0200, Jürgen Groß wrote:
On 15.10.24 11:58, Kirill A. Shutemov wrote:
AMD SEV-SNP and Intel TDX have limited access to MTRR: either it is not
advertised in CPUID or it cannot be programmed (on TDX, due to #VE on
CR0.CD clear).
This results in guests using uncached mappings where it shouldn't and
pmd/pud_set_huge() failures due to non-uniform memory type reported by
mtrr_type_lookup().
Override MTRR state, making it WB by default as the kernel does for
Hyper-V guests.
Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Suggested-by: Binbin Wu <binbin.wu@xxxxxxxxx>
Cc: Juergen Gross <jgross@xxxxxxxx>
Cc: Tom Lendacky <thomas.lendacky@xxxxxxx>
---
arch/x86/kernel/kvm.c | 4 ++++
1 file changed, 4 insertions(+)
diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
index 263f8aed4e2c..21e9e4845354 100644
--- a/arch/x86/kernel/kvm.c
+++ b/arch/x86/kernel/kvm.c
@@ -37,6 +37,7 @@
#include <asm/apic.h>
#include <asm/apicdef.h>
#include <asm/hypervisor.h>
+#include <asm/mtrr.h>
#include <asm/tlb.h>
#include <asm/cpuidle_haltpoll.h>
#include <asm/ptrace.h>
@@ -980,6 +981,9 @@ static void __init kvm_init_platform(void)
}
kvmclock_init();
x86_platform.apic_post_init = kvm_apic_init;
+
+ /* Set WB as the default cache mode for SEV-SNP and TDX */
+ mtrr_overwrite_state(NULL, 0, MTRR_TYPE_WRBACK);
Do you really want to do this for _all_ KVM guests?
I'd expect this call to be conditional on TDX or SEV-SNP.
mtrr_overwrite_state() checks it internally.
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