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x86/hyperv: Clean up hv_do_hypercall()

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What used to be a simple few instructions has turned into a giant mess
(for x86_64). Not only does it use static_branch wrong, it mixes it
with dynamic branches for no apparent reason.

Notably it uses static_branch through an out-of-line function call,
which completely defeats the purpose, since instead of a simple
JMP/NOP site, you get a CALL+RET+TEST+Jcc sequence in return, which is
absolutely idiotic.

Add to that a dynamic test of hyperv_paravisor_present, something
which is set once and never changed.

Replace all this idiocy with a single direct function call to the
right hypercall variant.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Michael Kelley <mhklinux@outlook.com>
Tested-by: Michael Kelley <mhklinux@outlook.com>
Acked-by: Sean Christopherson <seanjc@google.com>
Link: https://lkml.kernel.org/r/20250714103440.897136093@infradead.org
This commit is contained in:
Peter Zijlstra 2025-04-12 13:55:49 +02:00
parent a1d34a444c
commit 0e20f1f4c2
4 changed files with 89 additions and 102 deletions
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20
arch/x86/hyperv/hv_init.c
View File

@ -37,7 +37,27 @@
#include <linux/export.h>
void *hv_hypercall_pg;
#ifdef CONFIG_X86_64
u64 hv_std_hypercall(u64 control, u64 param1, u64 param2)
{
u64 hv_status;
if (!hv_hypercall_pg)
return U64_MAX;
register u64 __r8 asm("r8") = param2;
asm volatile (CALL_NOSPEC
: "=a" (hv_status), ASM_CALL_CONSTRAINT,
"+c" (control), "+d" (param1), "+r" (__r8)
: THUNK_TARGET(hv_hypercall_pg)
: "cc", "memory", "r9", "r10", "r11");
return hv_status;
}
#else
EXPORT_SYMBOL_GPL(hv_hypercall_pg);
#endif
union hv_ghcb * __percpu *hv_ghcb_pg;

15
arch/x86/hyperv/ivm.c
View File

@ -385,9 +385,23 @@ int hv_snp_boot_ap(u32 apic_id, unsigned long start_ip, unsigned int cpu)
return ret;
}
u64 hv_snp_hypercall(u64 control, u64 param1, u64 param2)
{
u64 hv_status;
register u64 __r8 asm("r8") = param2;
asm volatile("vmmcall"
: "=a" (hv_status), ASM_CALL_CONSTRAINT,
"+c" (control), "+d" (param1), "+r" (__r8)
: : "cc", "memory", "r9", "r10", "r11");
return hv_status;
}
#else
static inline void hv_ghcb_msr_write(u64 msr, u64 value) {}
static inline void hv_ghcb_msr_read(u64 msr, u64 *value) {}
u64 hv_snp_hypercall(u64 control, u64 param1, u64 param2) { return U64_MAX; }
#endif /* CONFIG_AMD_MEM_ENCRYPT */
#ifdef CONFIG_INTEL_TDX_GUEST
@ -437,6 +451,7 @@ u64 hv_tdx_hypercall(u64 control, u64 param1, u64 param2)
#else
static inline void hv_tdx_msr_write(u64 msr, u64 value) {}
static inline void hv_tdx_msr_read(u64 msr, u64 *value) {}
u64 hv_tdx_hypercall(u64 control, u64 param1, u64 param2) { return U64_MAX; }
#endif /* CONFIG_INTEL_TDX_GUEST */
#if defined(CONFIG_AMD_MEM_ENCRYPT) || defined(CONFIG_INTEL_TDX_GUEST)

137
arch/x86/include/asm/mshyperv.h
View File

@ -6,6 +6,7 @@
#include <linux/nmi.h>
#include <linux/msi.h>
#include <linux/io.h>
#include <linux/static_call.h>
#include <asm/nospec-branch.h>
#include <asm/paravirt.h>
#include <asm/msr.h>
@ -39,16 +40,21 @@ static inline unsigned char hv_get_nmi_reason(void)
return 0;
}
#if IS_ENABLED(CONFIG_HYPERV)
extern bool hyperv_paravisor_present;
extern u64 hv_tdx_hypercall(u64 control, u64 param1, u64 param2);
extern u64 hv_snp_hypercall(u64 control, u64 param1, u64 param2);
extern u64 hv_std_hypercall(u64 control, u64 param1, u64 param2);
#if IS_ENABLED(CONFIG_HYPERV)
extern void *hv_hypercall_pg;
extern union hv_ghcb * __percpu *hv_ghcb_pg;
bool hv_isolation_type_snp(void);
bool hv_isolation_type_tdx(void);
u64 hv_tdx_hypercall(u64 control, u64 param1, u64 param2);
#ifdef CONFIG_X86_64
DECLARE_STATIC_CALL(hv_hypercall, hv_std_hypercall);
#endif
/*
* DEFAULT INIT GPAT and SEGMENT LIMIT value in struct VMSA
@ -65,37 +71,15 @@ static inline u64 hv_do_hypercall(u64 control, void *input, void *output)
{
u64 input_address = input ? virt_to_phys(input) : 0;
u64 output_address = output ? virt_to_phys(output) : 0;
u64 hv_status;
#ifdef CONFIG_X86_64
if (hv_isolation_type_tdx() && !hyperv_paravisor_present)
return hv_tdx_hypercall(control, input_address, output_address);
if (hv_isolation_type_snp() && !hyperv_paravisor_present) {
__asm__ __volatile__("mov %[output_address], %%r8\n"
"vmmcall"
: "=a" (hv_status), ASM_CALL_CONSTRAINT,
"+c" (control), "+d" (input_address)
: [output_address] "r" (output_address)
: "cc", "memory", "r8", "r9", "r10", "r11");
return hv_status;
}
if (!hv_hypercall_pg)
return U64_MAX;
__asm__ __volatile__("mov %[output_address], %%r8\n"
CALL_NOSPEC
: "=a" (hv_status), ASM_CALL_CONSTRAINT,
"+c" (control), "+d" (input_address)
: [output_address] "r" (output_address),
THUNK_TARGET(hv_hypercall_pg)
: "cc", "memory", "r8", "r9", "r10", "r11");
return static_call_mod(hv_hypercall)(control, input_address, output_address);
#else
u32 input_address_hi = upper_32_bits(input_address);
u32 input_address_lo = lower_32_bits(input_address);
u32 output_address_hi = upper_32_bits(output_address);
u32 output_address_lo = lower_32_bits(output_address);
u64 hv_status;
if (!hv_hypercall_pg)
return U64_MAX;
@ -108,48 +92,30 @@ static inline u64 hv_do_hypercall(u64 control, void *input, void *output)
"D"(output_address_hi), "S"(output_address_lo),
THUNK_TARGET(hv_hypercall_pg)
: "cc", "memory");
#endif /* !x86_64 */
return hv_status;
#endif /* !x86_64 */
}
/* Fast hypercall with 8 bytes of input and no output */
static inline u64 _hv_do_fast_hypercall8(u64 control, u64 input1)
{
#ifdef CONFIG_X86_64
return static_call_mod(hv_hypercall)(control, input1, 0);
#else
u32 input1_hi = upper_32_bits(input1);
u32 input1_lo = lower_32_bits(input1);
u64 hv_status;
#ifdef CONFIG_X86_64
if (hv_isolation_type_tdx() && !hyperv_paravisor_present)
return hv_tdx_hypercall(control, input1, 0);
if (hv_isolation_type_snp() && !hyperv_paravisor_present) {
__asm__ __volatile__(
"vmmcall"
: "=a" (hv_status), ASM_CALL_CONSTRAINT,
"+c" (control), "+d" (input1)
:: "cc", "r8", "r9", "r10", "r11");
} else {
__asm__ __volatile__(CALL_NOSPEC
: "=a" (hv_status), ASM_CALL_CONSTRAINT,
"+c" (control), "+d" (input1)
: THUNK_TARGET(hv_hypercall_pg)
: "cc", "r8", "r9", "r10", "r11");
}
#else
{
u32 input1_hi = upper_32_bits(input1);
u32 input1_lo = lower_32_bits(input1);
__asm__ __volatile__ (CALL_NOSPEC
: "=A"(hv_status),
"+c"(input1_lo),
ASM_CALL_CONSTRAINT
: "A" (control),
"b" (input1_hi),
THUNK_TARGET(hv_hypercall_pg)
: "cc", "edi", "esi");
}
#endif
__asm__ __volatile__ (CALL_NOSPEC
: "=A"(hv_status),
"+c"(input1_lo),
ASM_CALL_CONSTRAINT
: "A" (control),
"b" (input1_hi),
THUNK_TARGET(hv_hypercall_pg)
: "cc", "edi", "esi");
return hv_status;
#endif
}
static inline u64 hv_do_fast_hypercall8(u16 code, u64 input1)
@ -162,45 +128,24 @@ static inline u64 hv_do_fast_hypercall8(u16 code, u64 input1)
/* Fast hypercall with 16 bytes of input */
static inline u64 _hv_do_fast_hypercall16(u64 control, u64 input1, u64 input2)
{
#ifdef CONFIG_X86_64
return static_call_mod(hv_hypercall)(control, input1, input2);
#else
u32 input1_hi = upper_32_bits(input1);
u32 input1_lo = lower_32_bits(input1);
u32 input2_hi = upper_32_bits(input2);
u32 input2_lo = lower_32_bits(input2);
u64 hv_status;
#ifdef CONFIG_X86_64
if (hv_isolation_type_tdx() && !hyperv_paravisor_present)
return hv_tdx_hypercall(control, input1, input2);
if (hv_isolation_type_snp() && !hyperv_paravisor_present) {
__asm__ __volatile__("mov %[input2], %%r8\n"
"vmmcall"
: "=a" (hv_status), ASM_CALL_CONSTRAINT,
"+c" (control), "+d" (input1)
: [input2] "r" (input2)
: "cc", "r8", "r9", "r10", "r11");
} else {
__asm__ __volatile__("mov %[input2], %%r8\n"
CALL_NOSPEC
: "=a" (hv_status), ASM_CALL_CONSTRAINT,
"+c" (control), "+d" (input1)
: [input2] "r" (input2),
THUNK_TARGET(hv_hypercall_pg)
: "cc", "r8", "r9", "r10", "r11");
}
#else
{
u32 input1_hi = upper_32_bits(input1);
u32 input1_lo = lower_32_bits(input1);
u32 input2_hi = upper_32_bits(input2);
u32 input2_lo = lower_32_bits(input2);
__asm__ __volatile__ (CALL_NOSPEC
: "=A"(hv_status),
"+c"(input1_lo), ASM_CALL_CONSTRAINT
: "A" (control), "b" (input1_hi),
"D"(input2_hi), "S"(input2_lo),
THUNK_TARGET(hv_hypercall_pg)
: "cc");
}
#endif
__asm__ __volatile__ (CALL_NOSPEC
: "=A"(hv_status),
"+c"(input1_lo), ASM_CALL_CONSTRAINT
: "A" (control), "b" (input1_hi),
"D"(input2_hi), "S"(input2_lo),
THUNK_TARGET(hv_hypercall_pg)
: "cc");
return hv_status;
#endif
}
static inline u64 hv_do_fast_hypercall16(u16 code, u64 input1, u64 input2)

19
arch/x86/kernel/cpu/mshyperv.c
View File

@ -38,10 +38,6 @@
bool hv_nested;
struct ms_hyperv_info ms_hyperv;
/* Used in modules via hv_do_hypercall(): see arch/x86/include/asm/mshyperv.h */
bool hyperv_paravisor_present __ro_after_init;
EXPORT_SYMBOL_GPL(hyperv_paravisor_present);
#if IS_ENABLED(CONFIG_HYPERV)
static inline unsigned int hv_get_nested_msr(unsigned int reg)
{
@ -288,8 +284,18 @@ static void __init x86_setup_ops_for_tsc_pg_clock(void)
old_restore_sched_clock_state = x86_platform.restore_sched_clock_state;
x86_platform.restore_sched_clock_state = hv_restore_sched_clock_state;
}
#ifdef CONFIG_X86_64
DEFINE_STATIC_CALL(hv_hypercall, hv_std_hypercall);
EXPORT_STATIC_CALL_TRAMP_GPL(hv_hypercall);
#define hypercall_update(hc) static_call_update(hv_hypercall, hc)
#endif
#endif /* CONFIG_HYPERV */
#ifndef hypercall_update
#define hypercall_update(hc) (void)hc
#endif
static uint32_t __init ms_hyperv_platform(void)
{
u32 eax;
@ -484,14 +490,14 @@ static void __init ms_hyperv_init_platform(void)
ms_hyperv.shared_gpa_boundary =
BIT_ULL(ms_hyperv.shared_gpa_boundary_bits);
hyperv_paravisor_present = !!ms_hyperv.paravisor_present;
pr_info("Hyper-V: Isolation Config: Group A 0x%x, Group B 0x%x\n",
ms_hyperv.isolation_config_a, ms_hyperv.isolation_config_b);
if (hv_get_isolation_type() == HV_ISOLATION_TYPE_SNP) {
static_branch_enable(&isolation_type_snp);
if (!ms_hyperv.paravisor_present)
hypercall_update(hv_snp_hypercall);
} else if (hv_get_isolation_type() == HV_ISOLATION_TYPE_TDX) {
static_branch_enable(&isolation_type_tdx);
@ -499,6 +505,7 @@ static void __init ms_hyperv_init_platform(void)
ms_hyperv.hints &= ~HV_X64_APIC_ACCESS_RECOMMENDED;
if (!ms_hyperv.paravisor_present) {
hypercall_update(hv_tdx_hypercall);
/*
* Mark the Hyper-V TSC page feature as disabled
* in a TDX VM without paravisor so that the