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Message-ID: <20231108111806.92604-6-nsaenz@amazon.com>
Date: Wed, 8 Nov 2023 11:17:38 +0000
From: Nicolas Saenz Julienne <nsaenz@...zon.com>
To: <kvm@...r.kernel.org>
CC: <linux-kernel@...r.kernel.org>, <linux-hyperv@...r.kernel.org>,
<pbonzini@...hat.com>, <seanjc@...gle.com>, <vkuznets@...hat.com>,
<anelkz@...zon.com>, <graf@...zon.com>, <dwmw@...zon.co.uk>,
<jgowans@...zon.com>, <corbert@....net>, <kys@...rosoft.com>,
<haiyangz@...rosoft.com>, <decui@...rosoft.com>, <x86@...nel.org>,
<linux-doc@...r.kernel.org>,
Nicolas Saenz Julienne <nsaenz@...zon.com>
Subject: [RFC 05/33] KVM: x86: hyper-v: Introduce VTL call/return prologues in hypercall page
VTL call/return hypercalls have their own entry points in the hypercall
page because they don't follow normal hyper-v hypercall conventions.
Move the VTL call/return control input into ECX/RAX and set the
hypercall code into EAX/RCX before calling the hypercall instruction in
order to be able to use the Hyper-V hypercall entry function.
Guests can read an emulated code page offsets register to know the
offsets into the hypercall page for the VTL call/return entries.
Signed-off-by: Nicolas Saenz Julienne <nsaenz@...zon.com>
---
My tree has the additional patch, we're still trying to understand under
what conditions Windows expects the offset to be fixed.
diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
index 54f7f36a89bf..9f2ea8c34447 100644
--- a/arch/x86/kvm/hyperv.c
+++ b/arch/x86/kvm/hyperv.c
@@ -294,6 +294,7 @@ static int patch_hypercall_page(struct kvm_vcpu *vcpu, u64 data)
/* VTL call/return entries */
if (!kvm_xen_hypercall_enabled(kvm) && kvm_hv_vsm_enabled(kvm)) {
+ i = 22;
#ifdef CONFIG_X86_64
if (is_64_bit_mode(vcpu)) {
/*
---
arch/x86/include/asm/kvm_host.h | 2 +
arch/x86/kvm/hyperv.c | 78 ++++++++++++++++++++++++++++++-
include/asm-generic/hyperv-tlfs.h | 11 +++++
3 files changed, 90 insertions(+), 1 deletion(-)
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index a2f224f95404..00cd21b09f8c 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -1105,6 +1105,8 @@ struct kvm_hv {
u64 hv_tsc_emulation_status;
u64 hv_invtsc_control;
+ union hv_register_vsm_code_page_offsets vsm_code_page_offsets;
+
/* How many vCPUs have VP index != vCPU index */
atomic_t num_mismatched_vp_indexes;
diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
index 78d053042667..d4b1b53ea63d 100644
--- a/arch/x86/kvm/hyperv.c
+++ b/arch/x86/kvm/hyperv.c
@@ -259,7 +259,8 @@ static void synic_exit(struct kvm_vcpu_hv_synic *synic, u32 msr)
static int patch_hypercall_page(struct kvm_vcpu *vcpu, u64 data)
{
struct kvm *kvm = vcpu->kvm;
- u8 instructions[9];
+ struct kvm_hv *hv = to_kvm_hv(kvm);
+ u8 instructions[0x30];
int i = 0;
u64 addr;
@@ -285,6 +286,81 @@ static int patch_hypercall_page(struct kvm_vcpu *vcpu, u64 data)
/* ret */
((unsigned char *)instructions)[i++] = 0xc3;
+ /* VTL call/return entries */
+ if (!kvm_xen_hypercall_enabled(kvm) && kvm_hv_vsm_enabled(kvm)) {
+#ifdef CONFIG_X86_64
+ if (is_64_bit_mode(vcpu)) {
+ /*
+ * VTL call 64-bit entry prologue:
+ * mov %rcx, %rax
+ * mov $0x11, %ecx
+ * jmp 0:
+ */
+ hv->vsm_code_page_offsets.vtl_call_offset = i;
+ instructions[i++] = 0x48;
+ instructions[i++] = 0x89;
+ instructions[i++] = 0xc8;
+ instructions[i++] = 0xb9;
+ instructions[i++] = 0x11;
+ instructions[i++] = 0x00;
+ instructions[i++] = 0x00;
+ instructions[i++] = 0x00;
+ instructions[i++] = 0xeb;
+ instructions[i++] = 0xe0;
+ /*
+ * VTL return 64-bit entry prologue:
+ * mov %rcx, %rax
+ * mov $0x12, %ecx
+ * jmp 0:
+ */
+ hv->vsm_code_page_offsets.vtl_return_offset = i;
+ instructions[i++] = 0x48;
+ instructions[i++] = 0x89;
+ instructions[i++] = 0xc8;
+ instructions[i++] = 0xb9;
+ instructions[i++] = 0x12;
+ instructions[i++] = 0x00;
+ instructions[i++] = 0x00;
+ instructions[i++] = 0x00;
+ instructions[i++] = 0xeb;
+ instructions[i++] = 0xd6;
+ } else
+#endif
+ {
+ /*
+ * VTL call 32-bit entry prologue:
+ * mov %eax, %ecx
+ * mov $0x11, %eax
+ * jmp 0:
+ */
+ hv->vsm_code_page_offsets.vtl_call_offset = i;
+ instructions[i++] = 0x89;
+ instructions[i++] = 0xc1;
+ instructions[i++] = 0xb8;
+ instructions[i++] = 0x11;
+ instructions[i++] = 0x00;
+ instructions[i++] = 0x00;
+ instructions[i++] = 0x00;
+ instructions[i++] = 0xeb;
+ instructions[i++] = 0xf3;
+ /*
+ * VTL return 32-bit entry prologue:
+ * mov %eax, %ecx
+ * mov $0x12, %eax
+ * jmp 0:
+ */
+ hv->vsm_code_page_offsets.vtl_return_offset = i;
+ instructions[i++] = 0x89;
+ instructions[i++] = 0xc1;
+ instructions[i++] = 0xb8;
+ instructions[i++] = 0x12;
+ instructions[i++] = 0x00;
+ instructions[i++] = 0x00;
+ instructions[i++] = 0x00;
+ instructions[i++] = 0xeb;
+ instructions[i++] = 0xea;
+ }
+ }
addr = data & HV_X64_MSR_HYPERCALL_PAGE_ADDRESS_MASK;
if (kvm_vcpu_write_guest(vcpu, addr, instructions, i))
return 1;
diff --git a/include/asm-generic/hyperv-tlfs.h b/include/asm-generic/hyperv-tlfs.h
index fdac4a1714ec..0e7643c1ef01 100644
--- a/include/asm-generic/hyperv-tlfs.h
+++ b/include/asm-generic/hyperv-tlfs.h
@@ -823,4 +823,15 @@ struct hv_mmio_write_input {
u8 data[HV_HYPERCALL_MMIO_MAX_DATA_LENGTH];
} __packed;
+/*
+ * VTL call/return hypercall page offsets register
+ */
+union hv_register_vsm_code_page_offsets {
+ u64 as_u64;
+ struct {
+ u64 vtl_call_offset:12;
+ u64 vtl_return_offset:12;
+ u64 reserved:40;
+ } __packed;
+};
#endif
--
2.40.1
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