On Wed, Apr 23, 2025, Manali Shukla wrote:
> On 4/16/2025 11:30 AM, Xiaoyao Li wrote:
> >> + if (cpu_feature_enabled(X86_FEATURE_BUS_LOCK_THRESHOLD)) {
> >> + pr_info("Bus Lock Threshold supported\n");
> >
> > It will be printed every time kvm-amd.ko module gets loaded.
> >
> > I think it's for your development and debug purpose. Comparing to the
> > existing features in svm_set_cpu_caps(), nothing makes it special for
> > BUS_LOCK_THRESHOLD to require a kernel message. So I think we can just
> > remove it.
>
> I didn't add this for development and debug purpose. I added this pr_info()
> to make it easy to find whether BUS Lock threshold is supported or not from
> dmesg. I can remove it if you think it is not required.
Please remove it. The user typically doesn't care.
> >> + kvm_caps.has_bus_lock_exit = true;
> >
> > Besides, this patch doesn't ensure the bisectability. It allows userspace
> > to enable KVM_BUS_LOCK_DETECTION_EXIT and set intercept of
> > INTERCEPT_BUSLOCK but without providing the handler.
> >
> > So either move next patch before it or just merge them.
> >
>
> Oh.., my bad, I will move the next patch before this one in v5.
No, do exactly as I suggested in v3.
: I vote to split this into two patches: one to add the architectural collateral,
: with the above as the changelog, and a second to actually implement support in
: KVM. Having the above background is useful, but it makes it quite hard to find
: information on the KVM design and implementation.
I want this (and any other arch collateral I'm missing) in a separate patch so
that the background on what the hardware feature does is captured. But I see no
reason to split KVM's implementation into multiple patches.
diff --git a/arch/x86/include/asm/svm.h b/arch/x86/include/asm/svm.h
index 2b59b9951c90..d1819c564b1c 100644
--- a/arch/x86/include/asm/svm.h
+++ b/arch/x86/include/asm/svm.h
@@ -116,6 +116,7 @@ enum {
INTERCEPT_INVPCID,
INTERCEPT_MCOMMIT,
INTERCEPT_TLBSYNC,
+ INTERCEPT_BUSLOCK,
};
@@ -158,7 +159,9 @@ struct __attribute__ ((__packed__)) vmcb_control_area {
u64 avic_physical_id; /* Offset 0xf8 */
u8 reserved_7[8];
u64 vmsa_pa; /* Used for an SEV-ES guest */
- u8 reserved_8[720];
+ u8 reserved_8[16];
+ u16 bus_lock_counter; /* Offset 0x120 */
+ u8 reserved_9[702];
/*
* Offset 0x3e0, 32 bytes reserved
* for use by hypervisor/software.
diff --git a/arch/x86/include/uapi/asm/svm.h b/arch/x86/include/uapi/asm/svm.h
index 1814b413fd57..abf6aed88cee 100644
--- a/arch/x86/include/uapi/asm/svm.h
+++ b/arch/x86/include/uapi/asm/svm.h
@@ -95,6 +95,7 @@
#define SVM_EXIT_CR14_WRITE_TRAP 0x09e
#define SVM_EXIT_CR15_WRITE_TRAP 0x09f
#define SVM_EXIT_INVPCID 0x0a2
+#define SVM_EXIT_BUS_LOCK 0x0a5
#define SVM_EXIT_NPF 0x400
#define SVM_EXIT_AVIC_INCOMPLETE_IPI 0x401
#define SVM_EXIT_AVIC_UNACCELERATED_ACCESS 0x402
@@ -224,6 +225,7 @@
{ SVM_EXIT_CR4_WRITE_TRAP, "write_cr4_trap" }, \
{ SVM_EXIT_CR8_WRITE_TRAP, "write_cr8_trap" }, \
{ SVM_EXIT_INVPCID, "invpcid" }, \
+ { SVM_EXIT_BUS_LOCK, "buslock" }, \
{ SVM_EXIT_NPF, "npf" }, \
{ SVM_EXIT_AVIC_INCOMPLETE_IPI, "avic_incomplete_ipi" }, \
{ SVM_EXIT_AVIC_UNACCELERATED_ACCESS, "avic_unaccelerated_access" }, \
