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Message-ID: <20250930070356.30695-12-jgross@suse.com>
Date: Tue, 30 Sep 2025 09:03:55 +0200
From: Juergen Gross <jgross@...e.com>
To: linux-kernel@...r.kernel.org,
x86@...nel.org,
virtualization@...ts.linux.dev
Cc: xin@...or.com,
Juergen Gross <jgross@...e.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>,
Ajay Kaher <ajay.kaher@...adcom.com>,
Alexey Makhalov <alexey.makhalov@...adcom.com>,
Broadcom internal kernel review list <bcm-kernel-feedback-list@...adcom.com>,
Boris Ostrovsky <boris.ostrovsky@...cle.com>,
xen-devel@...ts.xenproject.org
Subject: [PATCH v2 11/12] x86/paravirt: Don't use pv_ops vector for MSR access functions
Instead of using the pv_ops vector for RDMSR/WRMSR related functions,
use a more explicit approach allowing to inline the RDMSR/WRMSR
instructions directly when not running as a Xen PV guest.
By using cpu_feature_enabled(X86_FEATURE_XENPV) for the Xen PV case
the related calls to Xen specific code will be statically disabled via
runtime patching.
Signed-off-by: Juergen Gross <jgross@...e.com>
---
V2:
- new patch
---
arch/x86/include/asm/msr.h | 57 ++++++++++++++++++++++-----
arch/x86/include/asm/paravirt.h | 45 ---------------------
arch/x86/include/asm/paravirt_types.h | 13 ------
arch/x86/kernel/paravirt.c | 5 ---
arch/x86/xen/enlighten_pv.c | 20 ++++------
arch/x86/xen/pmu.c | 1 +
6 files changed, 57 insertions(+), 84 deletions(-)
diff --git a/arch/x86/include/asm/msr.h b/arch/x86/include/asm/msr.h
index cc592611e333..d42cd2c19818 100644
--- a/arch/x86/include/asm/msr.h
+++ b/arch/x86/include/asm/msr.h
@@ -290,24 +290,22 @@ static __always_inline void native_wrmsr(u32 msr, u32 low, u32 high)
native_wrmsrq(msr, (u64)high << 32 | low);
}
-static inline u64 native_read_msr(u32 msr)
+static __always_inline u64 native_read_msr(u32 msr)
{
return native_rdmsrq(msr);
}
-static inline int native_read_msr_safe(u32 msr, u64 *val)
+static __always_inline int native_read_msr_safe(u32 msr, u64 *val)
{
return __rdmsr(msr, val, EX_TYPE_RDMSR_SAFE) ? -EIO : 0;
}
-/* Can be uninlined because referenced by paravirt */
-static inline void notrace native_write_msr(u32 msr, u64 val)
+static __always_inline void native_write_msr(u32 msr, u64 val)
{
native_wrmsrq(msr, val);
}
-/* Can be uninlined because referenced by paravirt */
-static inline int notrace native_write_msr_safe(u32 msr, u64 val)
+static __always_inline int native_write_msr_safe(u32 msr, u64 val)
{
return __wrmsrq(msr, val, EX_TYPE_WRMSR_SAFE) ? -EIO : 0;
}
@@ -325,8 +323,49 @@ static inline u64 native_read_pmc(int counter)
return EAX_EDX_VAL(val, low, high);
}
-#ifdef CONFIG_PARAVIRT_XXL
-#include <asm/paravirt.h>
+#ifdef CONFIG_XEN_PV
+#include <asm/xen/msr.h>
+
+static __always_inline u64 read_msr(u32 msr)
+{
+ if (cpu_feature_enabled(X86_FEATURE_XENPV))
+ return xen_read_msr(msr);
+
+ return native_rdmsrq(msr);
+}
+
+static __always_inline int read_msr_safe(u32 msr, u64 *p)
+{
+ if (cpu_feature_enabled(X86_FEATURE_XENPV))
+ return xen_read_msr_safe(msr, p);
+
+ return native_read_msr_safe(msr, p);
+}
+
+static __always_inline void write_msr(u32 msr, u64 val)
+{
+ if (cpu_feature_enabled(X86_FEATURE_XENPV))
+ xen_write_msr(msr, val);
+ else
+ native_wrmsrq(msr, val);
+}
+
+static __always_inline int write_msr_safe(u32 msr, u64 val)
+{
+ if (cpu_feature_enabled(X86_FEATURE_XENPV))
+ return xen_write_msr_safe(msr, val);
+
+ return native_write_msr_safe(msr, val);
+}
+
+static __always_inline u64 rdpmc(int counter)
+{
+ if (cpu_feature_enabled(X86_FEATURE_XENPV))
+ return xen_read_pmc(counter);
+
+ return native_read_pmc(counter);
+}
+
#else
static __always_inline u64 read_msr(u32 msr)
{
@@ -353,7 +392,7 @@ static __always_inline u64 rdpmc(int counter)
return native_read_pmc(counter);
}
-#endif /* !CONFIG_PARAVIRT_XXL */
+#endif /* !CONFIG_XEN_PV */
/*
* Access to machine-specific registers (available on 586 and better only)
diff --git a/arch/x86/include/asm/paravirt.h b/arch/x86/include/asm/paravirt.h
index dc297f62b935..45f47b7d9f56 100644
--- a/arch/x86/include/asm/paravirt.h
+++ b/arch/x86/include/asm/paravirt.h
@@ -175,51 +175,6 @@ static inline void __write_cr4(unsigned long x)
PVOP_VCALL1(cpu.write_cr4, x);
}
-static inline u64 paravirt_read_msr(u32 msr)
-{
- return PVOP_CALL1(u64, cpu.read_msr, msr);
-}
-
-static inline void paravirt_write_msr(u32 msr, u64 val)
-{
- PVOP_VCALL2(cpu.write_msr, msr, val);
-}
-
-static inline int paravirt_read_msr_safe(u32 msr, u64 *val)
-{
- return PVOP_CALL2(int, cpu.read_msr_safe, msr, val);
-}
-
-static inline int paravirt_write_msr_safe(u32 msr, u64 val)
-{
- return PVOP_CALL2(int, cpu.write_msr_safe, msr, val);
-}
-
-static __always_inline u64 read_msr(u32 msr)
-{
- return paravirt_read_msr(msr);
-}
-
-static __always_inline int read_msr_safe(u32 msr, u64 *p)
-{
- return paravirt_read_msr_safe(msr, p);
-}
-
-static __always_inline void write_msr(u32 msr, u64 val)
-{
- paravirt_write_msr(msr, val);
-}
-
-static __always_inline int write_msr_safe(u32 msr, u64 val)
-{
- return paravirt_write_msr_safe(msr, val);
-}
-
-static __always_inline u64 rdpmc(int counter)
-{
- return PVOP_CALL1(u64, cpu.read_pmc, counter);
-}
-
static inline void paravirt_alloc_ldt(struct desc_struct *ldt, unsigned entries)
{
PVOP_VCALL2(cpu.alloc_ldt, ldt, entries);
diff --git a/arch/x86/include/asm/paravirt_types.h b/arch/x86/include/asm/paravirt_types.h
index 37a8627d8277..0d03e658ea8f 100644
--- a/arch/x86/include/asm/paravirt_types.h
+++ b/arch/x86/include/asm/paravirt_types.h
@@ -90,19 +90,6 @@ struct pv_cpu_ops {
void (*cpuid)(unsigned int *eax, unsigned int *ebx,
unsigned int *ecx, unsigned int *edx);
- /* Unsafe MSR operations. These will warn or panic on failure. */
- u64 (*read_msr)(u32 msr);
- void (*write_msr)(u32 msr, u64 val);
-
- /*
- * Safe MSR operations.
- * Returns 0 or -EIO.
- */
- int (*read_msr_safe)(u32 msr, u64 *val);
- int (*write_msr_safe)(u32 msr, u64 val);
-
- u64 (*read_pmc)(int counter);
-
void (*start_context_switch)(struct task_struct *prev);
void (*end_context_switch)(struct task_struct *next);
#endif
diff --git a/arch/x86/kernel/paravirt.c b/arch/x86/kernel/paravirt.c
index ab3e172dcc69..240eeb1beab5 100644
--- a/arch/x86/kernel/paravirt.c
+++ b/arch/x86/kernel/paravirt.c
@@ -129,11 +129,6 @@ struct paravirt_patch_template pv_ops = {
.cpu.read_cr0 = native_read_cr0,
.cpu.write_cr0 = native_write_cr0,
.cpu.write_cr4 = native_write_cr4,
- .cpu.read_msr = native_read_msr,
- .cpu.write_msr = native_write_msr,
- .cpu.read_msr_safe = native_read_msr_safe,
- .cpu.write_msr_safe = native_write_msr_safe,
- .cpu.read_pmc = native_read_pmc,
.cpu.load_tr_desc = native_load_tr_desc,
.cpu.set_ldt = native_set_ldt,
.cpu.load_gdt = native_load_gdt,
diff --git a/arch/x86/xen/enlighten_pv.c b/arch/x86/xen/enlighten_pv.c
index 26bbaf4b7330..df653099c567 100644
--- a/arch/x86/xen/enlighten_pv.c
+++ b/arch/x86/xen/enlighten_pv.c
@@ -1160,15 +1160,16 @@ static void xen_do_write_msr(u32 msr, u64 val, int *err)
}
}
-static int xen_read_msr_safe(u32 msr, u64 *val)
+int xen_read_msr_safe(u32 msr, u64 *val)
{
int err = 0;
*val = xen_do_read_msr(msr, &err);
return err;
}
+EXPORT_SYMBOL(xen_read_msr_safe);
-static int xen_write_msr_safe(u32 msr, u64 val)
+int xen_write_msr_safe(u32 msr, u64 val)
{
int err = 0;
@@ -1176,20 +1177,23 @@ static int xen_write_msr_safe(u32 msr, u64 val)
return err;
}
+EXPORT_SYMBOL(xen_write_msr_safe);
-static u64 xen_read_msr(u32 msr)
+u64 xen_read_msr(u32 msr)
{
int err = 0;
return xen_do_read_msr(msr, xen_msr_safe ? &err : NULL);
}
+EXPORT_SYMBOL(xen_read_msr);
-static void xen_write_msr(u32 msr, u64 val)
+void xen_write_msr(u32 msr, u64 val)
{
int err;
xen_do_write_msr(msr, val, xen_msr_safe ? &err : NULL);
}
+EXPORT_SYMBOL(xen_write_msr);
/* This is called once we have the cpu_possible_mask */
void __init xen_setup_vcpu_info_placement(void)
@@ -1225,14 +1229,6 @@ static const typeof(pv_ops) xen_cpu_ops __initconst = {
.write_cr4 = xen_write_cr4,
- .read_msr = xen_read_msr,
- .write_msr = xen_write_msr,
-
- .read_msr_safe = xen_read_msr_safe,
- .write_msr_safe = xen_write_msr_safe,
-
- .read_pmc = xen_read_pmc,
-
.load_tr_desc = paravirt_nop,
.set_ldt = xen_set_ldt,
.load_gdt = xen_load_gdt,
diff --git a/arch/x86/xen/pmu.c b/arch/x86/xen/pmu.c
index d49a3bdc448b..d0dea950cd4f 100644
--- a/arch/x86/xen/pmu.c
+++ b/arch/x86/xen/pmu.c
@@ -370,6 +370,7 @@ u64 xen_read_pmc(int counter)
else
return xen_intel_read_pmc(counter);
}
+EXPORT_SYMBOL(xen_read_pmc);
int pmu_apic_update(uint32_t val)
{
--
2.51.0
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