* [PATCH v2 2/8] KVM: SVM: replace regs argument of __svm_vcpu_run with vcpu_svm
[not found] <20221108151532.1377783-1-pbonzini@redhat.com>
@ 2022-11-08 15:15 ` Paolo Bonzini
2022-11-08 20:54 ` Sean Christopherson
2022-11-08 15:15 ` [PATCH v2 3/8] KVM: SVM: adjust register allocation for __svm_vcpu_run Paolo Bonzini
` (4 subsequent siblings)
5 siblings, 1 reply; 13+ messages in thread
From: Paolo Bonzini @ 2022-11-08 15:15 UTC (permalink / raw)
To: linux-kernel, kvm
Cc: nathan, thomas.lendacky, andrew.cooper3, peterz, jmattson,
seanjc, stable
Since registers are reachable through vcpu_svm, and we will
need to access more fields of that struct, pass it instead
of the regs[] array.
No functional change intended.
Cc: stable@vger.kernel.org
Fixes: f14eec0a3203 ("KVM: SVM: move more vmentry code to assembly")
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
arch/x86/kvm/Makefile | 3 +++
arch/x86/kvm/kvm-asm-offsets.c | 6 ++++++
arch/x86/kvm/svm/svm.c | 2 +-
arch/x86/kvm/svm/svm.h | 2 +-
arch/x86/kvm/svm/vmenter.S | 37 +++++++++++++++++-----------------
5 files changed, 30 insertions(+), 20 deletions(-)
diff --git a/arch/x86/kvm/Makefile b/arch/x86/kvm/Makefile
index a02cf9baacc8..f453a0f96e24 100644
--- a/arch/x86/kvm/Makefile
+++ b/arch/x86/kvm/Makefile
@@ -35,6 +35,9 @@ obj-$(CONFIG_KVM) += kvm.o
obj-$(CONFIG_KVM_INTEL) += kvm-intel.o
obj-$(CONFIG_KVM_AMD) += kvm-amd.o
+AFLAGS_svm/vmenter.o := -iquote $(obj)
+$(obj)/svm/vmenter.o: $(obj)/kvm-asm-offsets.h
+
AFLAGS_vmx/vmenter.o := -iquote $(obj)
$(obj)/vmx/vmenter.o: $(obj)/kvm-asm-offsets.h
diff --git a/arch/x86/kvm/kvm-asm-offsets.c b/arch/x86/kvm/kvm-asm-offsets.c
index 9d84f2b32d7f..30db96852e2d 100644
--- a/arch/x86/kvm/kvm-asm-offsets.c
+++ b/arch/x86/kvm/kvm-asm-offsets.c
@@ -8,9 +8,15 @@
#include <linux/kbuild.h>
#include "vmx/vmx.h"
+#include "svm/svm.h"
static void __used common(void)
{
+ if (IS_ENABLED(CONFIG_KVM_AMD)) {
+ BLANK();
+ OFFSET(SVM_vcpu_arch_regs, vcpu_svm, vcpu.arch.regs);
+ }
+
if (IS_ENABLED(CONFIG_KVM_INTEL)) {
BLANK();
OFFSET(VMX_spec_ctrl, vcpu_vmx, spec_ctrl);
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 58f0077d9357..b412bc5773c5 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -3930,7 +3930,7 @@ static noinstr void svm_vcpu_enter_exit(struct kvm_vcpu *vcpu)
* vmcb02 when switching vmcbs for nested virtualization.
*/
vmload(svm->vmcb01.pa);
- __svm_vcpu_run(vmcb_pa, (unsigned long *)&vcpu->arch.regs);
+ __svm_vcpu_run(vmcb_pa, svm);
vmsave(svm->vmcb01.pa);
vmload(__sme_page_pa(sd->save_area));
diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
index 6a7686bf6900..447e25c9101a 100644
--- a/arch/x86/kvm/svm/svm.h
+++ b/arch/x86/kvm/svm/svm.h
@@ -684,6 +684,6 @@ void sev_es_unmap_ghcb(struct vcpu_svm *svm);
/* vmenter.S */
void __svm_sev_es_vcpu_run(unsigned long vmcb_pa);
-void __svm_vcpu_run(unsigned long vmcb_pa, unsigned long *regs);
+void __svm_vcpu_run(unsigned long vmcb_pa, struct vcpu_svm *svm);
#endif
diff --git a/arch/x86/kvm/svm/vmenter.S b/arch/x86/kvm/svm/vmenter.S
index 723f8534986c..f0ff41103e4c 100644
--- a/arch/x86/kvm/svm/vmenter.S
+++ b/arch/x86/kvm/svm/vmenter.S
@@ -4,27 +4,28 @@
#include <asm/bitsperlong.h>
#include <asm/kvm_vcpu_regs.h>
#include <asm/nospec-branch.h>
+#include "kvm-asm-offsets.h"
#define WORD_SIZE (BITS_PER_LONG / 8)
/* Intentionally omit RAX as it's context switched by hardware */
-#define VCPU_RCX __VCPU_REGS_RCX * WORD_SIZE
-#define VCPU_RDX __VCPU_REGS_RDX * WORD_SIZE
-#define VCPU_RBX __VCPU_REGS_RBX * WORD_SIZE
+#define VCPU_RCX (SVM_vcpu_arch_regs + __VCPU_REGS_RCX * WORD_SIZE)
+#define VCPU_RDX (SVM_vcpu_arch_regs + __VCPU_REGS_RDX * WORD_SIZE)
+#define VCPU_RBX (SVM_vcpu_arch_regs + __VCPU_REGS_RBX * WORD_SIZE)
/* Intentionally omit RSP as it's context switched by hardware */
-#define VCPU_RBP __VCPU_REGS_RBP * WORD_SIZE
-#define VCPU_RSI __VCPU_REGS_RSI * WORD_SIZE
-#define VCPU_RDI __VCPU_REGS_RDI * WORD_SIZE
+#define VCPU_RBP (SVM_vcpu_arch_regs + __VCPU_REGS_RBP * WORD_SIZE)
+#define VCPU_RSI (SVM_vcpu_arch_regs + __VCPU_REGS_RSI * WORD_SIZE)
+#define VCPU_RDI (SVM_vcpu_arch_regs + __VCPU_REGS_RDI * WORD_SIZE)
#ifdef CONFIG_X86_64
-#define VCPU_R8 __VCPU_REGS_R8 * WORD_SIZE
-#define VCPU_R9 __VCPU_REGS_R9 * WORD_SIZE
-#define VCPU_R10 __VCPU_REGS_R10 * WORD_SIZE
-#define VCPU_R11 __VCPU_REGS_R11 * WORD_SIZE
-#define VCPU_R12 __VCPU_REGS_R12 * WORD_SIZE
-#define VCPU_R13 __VCPU_REGS_R13 * WORD_SIZE
-#define VCPU_R14 __VCPU_REGS_R14 * WORD_SIZE
-#define VCPU_R15 __VCPU_REGS_R15 * WORD_SIZE
+#define VCPU_R8 (SVM_vcpu_arch_regs + __VCPU_REGS_R8 * WORD_SIZE)
+#define VCPU_R9 (SVM_vcpu_arch_regs + __VCPU_REGS_R9 * WORD_SIZE)
+#define VCPU_R10 (SVM_vcpu_arch_regs + __VCPU_REGS_R10 * WORD_SIZE)
+#define VCPU_R11 (SVM_vcpu_arch_regs + __VCPU_REGS_R11 * WORD_SIZE)
+#define VCPU_R12 (SVM_vcpu_arch_regs + __VCPU_REGS_R12 * WORD_SIZE)
+#define VCPU_R13 (SVM_vcpu_arch_regs + __VCPU_REGS_R13 * WORD_SIZE)
+#define VCPU_R14 (SVM_vcpu_arch_regs + __VCPU_REGS_R14 * WORD_SIZE)
+#define VCPU_R15 (SVM_vcpu_arch_regs + __VCPU_REGS_R15 * WORD_SIZE)
#endif
.section .noinstr.text, "ax"
@@ -32,7 +33,7 @@
/**
* __svm_vcpu_run - Run a vCPU via a transition to SVM guest mode
* @vmcb_pa: unsigned long
- * @regs: unsigned long * (to guest registers)
+ * @svm: struct vcpu_svm *
*/
SYM_FUNC_START(__svm_vcpu_run)
push %_ASM_BP
@@ -47,13 +48,13 @@ SYM_FUNC_START(__svm_vcpu_run)
#endif
push %_ASM_BX
- /* Save @regs. */
+ /* Save @svm. */
push %_ASM_ARG2
/* Save @vmcb. */
push %_ASM_ARG1
- /* Move @regs to RAX. */
+ /* Move @svm to RAX. */
mov %_ASM_ARG2, %_ASM_AX
/* Load guest registers. */
@@ -89,7 +90,7 @@ SYM_FUNC_START(__svm_vcpu_run)
FILL_RETURN_BUFFER %_ASM_AX, RSB_CLEAR_LOOPS, X86_FEATURE_RETPOLINE
#endif
- /* "POP" @regs to RAX. */
+ /* "POP" @svm to RAX. */
pop %_ASM_AX
/* Save all guest registers. */
--
2.31.1
^ permalink raw reply related [flat|nested] 13+ messages in thread
* [PATCH v2 3/8] KVM: SVM: adjust register allocation for __svm_vcpu_run
[not found] <20221108151532.1377783-1-pbonzini@redhat.com>
2022-11-08 15:15 ` [PATCH v2 2/8] KVM: SVM: replace regs argument of __svm_vcpu_run with vcpu_svm Paolo Bonzini
@ 2022-11-08 15:15 ` Paolo Bonzini
2022-11-08 20:55 ` Sean Christopherson
2022-11-08 15:15 ` [PATCH v2 4/8] KVM: SVM: retrieve VMCB from assembly Paolo Bonzini
` (3 subsequent siblings)
5 siblings, 1 reply; 13+ messages in thread
From: Paolo Bonzini @ 2022-11-08 15:15 UTC (permalink / raw)
To: linux-kernel, kvm
Cc: nathan, thomas.lendacky, andrew.cooper3, peterz, jmattson,
seanjc, stable
In preparation for moving vmload/vmsave to __svm_vcpu_run,
keep the pointer to the struct vcpu_svm in %rdi. This way
it is possible to load svm->vmcb01.pa in %rax without
clobbering the pointer to svm itself.
No functional change intended.
Cc: stable@vger.kernel.org
Fixes: f14eec0a3203 ("KVM: SVM: move more vmentry code to assembly")
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
arch/x86/kvm/svm/vmenter.S | 38 +++++++++++++++++++-------------------
1 file changed, 19 insertions(+), 19 deletions(-)
diff --git a/arch/x86/kvm/svm/vmenter.S b/arch/x86/kvm/svm/vmenter.S
index f0ff41103e4c..531510ab6072 100644
--- a/arch/x86/kvm/svm/vmenter.S
+++ b/arch/x86/kvm/svm/vmenter.S
@@ -54,29 +54,29 @@ SYM_FUNC_START(__svm_vcpu_run)
/* Save @vmcb. */
push %_ASM_ARG1
- /* Move @svm to RAX. */
- mov %_ASM_ARG2, %_ASM_AX
+ /* Move @svm to RDI. */
+ mov %_ASM_ARG2, %_ASM_DI
+
+ /* "POP" @vmcb to RAX. */
+ pop %_ASM_AX
/* Load guest registers. */
- mov VCPU_RCX(%_ASM_AX), %_ASM_CX
- mov VCPU_RDX(%_ASM_AX), %_ASM_DX
- mov VCPU_RBX(%_ASM_AX), %_ASM_BX
- mov VCPU_RBP(%_ASM_AX), %_ASM_BP
- mov VCPU_RSI(%_ASM_AX), %_ASM_SI
- mov VCPU_RDI(%_ASM_AX), %_ASM_DI
+ mov VCPU_RCX(%_ASM_DI), %_ASM_CX
+ mov VCPU_RDX(%_ASM_DI), %_ASM_DX
+ mov VCPU_RBX(%_ASM_DI), %_ASM_BX
+ mov VCPU_RBP(%_ASM_DI), %_ASM_BP
+ mov VCPU_RSI(%_ASM_DI), %_ASM_SI
#ifdef CONFIG_X86_64
- mov VCPU_R8 (%_ASM_AX), %r8
- mov VCPU_R9 (%_ASM_AX), %r9
- mov VCPU_R10(%_ASM_AX), %r10
- mov VCPU_R11(%_ASM_AX), %r11
- mov VCPU_R12(%_ASM_AX), %r12
- mov VCPU_R13(%_ASM_AX), %r13
- mov VCPU_R14(%_ASM_AX), %r14
- mov VCPU_R15(%_ASM_AX), %r15
+ mov VCPU_R8 (%_ASM_DI), %r8
+ mov VCPU_R9 (%_ASM_DI), %r9
+ mov VCPU_R10(%_ASM_DI), %r10
+ mov VCPU_R11(%_ASM_DI), %r11
+ mov VCPU_R12(%_ASM_DI), %r12
+ mov VCPU_R13(%_ASM_DI), %r13
+ mov VCPU_R14(%_ASM_DI), %r14
+ mov VCPU_R15(%_ASM_DI), %r15
#endif
-
- /* "POP" @vmcb to RAX. */
- pop %_ASM_AX
+ mov VCPU_RDI(%_ASM_DI), %_ASM_DI
/* Enter guest mode */
sti
--
2.31.1
^ permalink raw reply related [flat|nested] 13+ messages in thread
* [PATCH v2 4/8] KVM: SVM: retrieve VMCB from assembly
[not found] <20221108151532.1377783-1-pbonzini@redhat.com>
2022-11-08 15:15 ` [PATCH v2 2/8] KVM: SVM: replace regs argument of __svm_vcpu_run with vcpu_svm Paolo Bonzini
2022-11-08 15:15 ` [PATCH v2 3/8] KVM: SVM: adjust register allocation for __svm_vcpu_run Paolo Bonzini
@ 2022-11-08 15:15 ` Paolo Bonzini
2022-11-09 0:53 ` Sean Christopherson
2022-11-08 15:15 ` [PATCH v2 5/8] KVM: SVM: move guest vmsave/vmload to assembly Paolo Bonzini
` (2 subsequent siblings)
5 siblings, 1 reply; 13+ messages in thread
From: Paolo Bonzini @ 2022-11-08 15:15 UTC (permalink / raw)
To: linux-kernel, kvm
Cc: nathan, thomas.lendacky, andrew.cooper3, peterz, jmattson,
seanjc, stable
This is needed in order to keep the number of arguments to 3 or less,
after adding hsave_pa and spec_ctrl_intercepted. 32-bit builds only
support passing three arguments in registers, fortunately all other
data is reachable from the vcpu_svm struct.
It is not strictly necessary for __svm_sev_es_vcpu_run, but staying
consistent is a good idea since it makes __svm_sev_es_vcpu_run a
stripped version of _svm_vcpu_run.
No functional change intended.
Cc: stable@vger.kernel.org
Fixes: f14eec0a3203 ("KVM: SVM: move more vmentry code to assembly")
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
arch/x86/kvm/kvm-asm-offsets.c | 2 ++
arch/x86/kvm/svm/svm.c | 5 ++---
arch/x86/kvm/svm/svm.h | 4 ++--
arch/x86/kvm/svm/vmenter.S | 20 ++++++++++----------
4 files changed, 16 insertions(+), 15 deletions(-)
diff --git a/arch/x86/kvm/kvm-asm-offsets.c b/arch/x86/kvm/kvm-asm-offsets.c
index 30db96852e2d..f1b694e431ae 100644
--- a/arch/x86/kvm/kvm-asm-offsets.c
+++ b/arch/x86/kvm/kvm-asm-offsets.c
@@ -15,6 +15,8 @@ static void __used common(void)
if (IS_ENABLED(CONFIG_KVM_AMD)) {
BLANK();
OFFSET(SVM_vcpu_arch_regs, vcpu_svm, vcpu.arch.regs);
+ OFFSET(SVM_current_vmcb, vcpu_svm, current_vmcb);
+ OFFSET(KVM_VMCB_pa, kvm_vmcb_info, pa);
}
if (IS_ENABLED(CONFIG_KVM_INTEL)) {
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index b412bc5773c5..0c86c435c51f 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -3914,12 +3914,11 @@ static fastpath_t svm_exit_handlers_fastpath(struct kvm_vcpu *vcpu)
static noinstr void svm_vcpu_enter_exit(struct kvm_vcpu *vcpu)
{
struct vcpu_svm *svm = to_svm(vcpu);
- unsigned long vmcb_pa = svm->current_vmcb->pa;
guest_state_enter_irqoff();
if (sev_es_guest(vcpu->kvm)) {
- __svm_sev_es_vcpu_run(vmcb_pa);
+ __svm_sev_es_vcpu_run(svm);
} else {
struct svm_cpu_data *sd = per_cpu(svm_data, vcpu->cpu);
@@ -3930,7 +3929,7 @@ static noinstr void svm_vcpu_enter_exit(struct kvm_vcpu *vcpu)
* vmcb02 when switching vmcbs for nested virtualization.
*/
vmload(svm->vmcb01.pa);
- __svm_vcpu_run(vmcb_pa, svm);
+ __svm_vcpu_run(svm);
vmsave(svm->vmcb01.pa);
vmload(__sme_page_pa(sd->save_area));
diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
index 447e25c9101a..7ff1879e73c5 100644
--- a/arch/x86/kvm/svm/svm.h
+++ b/arch/x86/kvm/svm/svm.h
@@ -683,7 +683,7 @@ void sev_es_unmap_ghcb(struct vcpu_svm *svm);
/* vmenter.S */
-void __svm_sev_es_vcpu_run(unsigned long vmcb_pa);
-void __svm_vcpu_run(unsigned long vmcb_pa, struct vcpu_svm *svm);
+void __svm_sev_es_vcpu_run(struct vcpu_svm *svm);
+void __svm_vcpu_run(struct vcpu_svm *svm);
#endif
diff --git a/arch/x86/kvm/svm/vmenter.S b/arch/x86/kvm/svm/vmenter.S
index 531510ab6072..d07bac1952c5 100644
--- a/arch/x86/kvm/svm/vmenter.S
+++ b/arch/x86/kvm/svm/vmenter.S
@@ -32,7 +32,6 @@
/**
* __svm_vcpu_run - Run a vCPU via a transition to SVM guest mode
- * @vmcb_pa: unsigned long
* @svm: struct vcpu_svm *
*/
SYM_FUNC_START(__svm_vcpu_run)
@@ -49,16 +48,16 @@ SYM_FUNC_START(__svm_vcpu_run)
push %_ASM_BX
/* Save @svm. */
- push %_ASM_ARG2
-
- /* Save @vmcb. */
push %_ASM_ARG1
+.ifnc _ASM_ARG1, _ASM_DI
/* Move @svm to RDI. */
- mov %_ASM_ARG2, %_ASM_DI
+ mov %_ASM_ARG1, %_ASM_DI
+.endif
- /* "POP" @vmcb to RAX. */
- pop %_ASM_AX
+ /* Get svm->current_vmcb->pa into RAX. */
+ mov SVM_current_vmcb(%_ASM_DI), %_ASM_AX
+ mov KVM_VMCB_pa(%_ASM_AX), %_ASM_AX
/* Load guest registers. */
mov VCPU_RCX(%_ASM_DI), %_ASM_CX
@@ -170,7 +169,7 @@ SYM_FUNC_END(__svm_vcpu_run)
/**
* __svm_sev_es_vcpu_run - Run a SEV-ES vCPU via a transition to SVM guest mode
- * @vmcb_pa: unsigned long
+ * @svm: struct vcpu_svm *
*/
SYM_FUNC_START(__svm_sev_es_vcpu_run)
push %_ASM_BP
@@ -185,8 +184,9 @@ SYM_FUNC_START(__svm_sev_es_vcpu_run)
#endif
push %_ASM_BX
- /* Move @vmcb to RAX. */
- mov %_ASM_ARG1, %_ASM_AX
+ /* Get svm->current_vmcb->pa into RAX. */
+ mov SVM_current_vmcb(%_ASM_ARG1), %_ASM_AX
+ mov KVM_VMCB_pa(%_ASM_AX), %_ASM_AX
/* Enter guest mode */
sti
--
2.31.1
^ permalink raw reply related [flat|nested] 13+ messages in thread
* [PATCH v2 5/8] KVM: SVM: move guest vmsave/vmload to assembly
[not found] <20221108151532.1377783-1-pbonzini@redhat.com>
` (2 preceding siblings ...)
2022-11-08 15:15 ` [PATCH v2 4/8] KVM: SVM: retrieve VMCB from assembly Paolo Bonzini
@ 2022-11-08 15:15 ` Paolo Bonzini
2022-11-08 15:15 ` [PATCH v2 6/8] KVM: SVM: restore host save area from assembly Paolo Bonzini
2022-11-08 15:15 ` [PATCH v2 7/8] KVM: SVM: move MSR_IA32_SPEC_CTRL save/restore to assembly Paolo Bonzini
5 siblings, 0 replies; 13+ messages in thread
From: Paolo Bonzini @ 2022-11-08 15:15 UTC (permalink / raw)
To: linux-kernel, kvm
Cc: nathan, thomas.lendacky, andrew.cooper3, peterz, jmattson,
seanjc, stable
FILL_RETURN_BUFFER can access percpu data, therefore vmload of the
host save area must be executed first. First of all, move the
VMCB vmsave/vmload to assembly.
The idea on how to number the exception tables is stolen from
a prototype patch by Peter Zijlstra.
Cc: stable@vger.kernel.org
Fixes: f14eec0a3203 ("KVM: SVM: move more vmentry code to assembly")
Link: <https://lore.kernel.org/all/f571e404-e625-bae1-10e9-449b2eb4cbd8@citrix.com/>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
arch/x86/kvm/kvm-asm-offsets.c | 1 +
arch/x86/kvm/svm/svm.c | 9 -------
arch/x86/kvm/svm/vmenter.S | 49 ++++++++++++++++++++++++++--------
3 files changed, 39 insertions(+), 20 deletions(-)
diff --git a/arch/x86/kvm/kvm-asm-offsets.c b/arch/x86/kvm/kvm-asm-offsets.c
index f1b694e431ae..f83e88b85bf2 100644
--- a/arch/x86/kvm/kvm-asm-offsets.c
+++ b/arch/x86/kvm/kvm-asm-offsets.c
@@ -16,6 +16,7 @@ static void __used common(void)
BLANK();
OFFSET(SVM_vcpu_arch_regs, vcpu_svm, vcpu.arch.regs);
OFFSET(SVM_current_vmcb, vcpu_svm, current_vmcb);
+ OFFSET(SVM_vmcb01, vcpu_svm, vmcb01);
OFFSET(KVM_VMCB_pa, kvm_vmcb_info, pa);
}
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 0c86c435c51f..0ba4feb19cb6 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -3922,16 +3922,7 @@ static noinstr void svm_vcpu_enter_exit(struct kvm_vcpu *vcpu)
} else {
struct svm_cpu_data *sd = per_cpu(svm_data, vcpu->cpu);
- /*
- * Use a single vmcb (vmcb01 because it's always valid) for
- * context switching guest state via VMLOAD/VMSAVE, that way
- * the state doesn't need to be copied between vmcb01 and
- * vmcb02 when switching vmcbs for nested virtualization.
- */
- vmload(svm->vmcb01.pa);
__svm_vcpu_run(svm);
- vmsave(svm->vmcb01.pa);
-
vmload(__sme_page_pa(sd->save_area));
}
diff --git a/arch/x86/kvm/svm/vmenter.S b/arch/x86/kvm/svm/vmenter.S
index d07bac1952c5..5bc2ed7d79c0 100644
--- a/arch/x86/kvm/svm/vmenter.S
+++ b/arch/x86/kvm/svm/vmenter.S
@@ -28,6 +28,8 @@
#define VCPU_R15 (SVM_vcpu_arch_regs + __VCPU_REGS_R15 * WORD_SIZE)
#endif
+#define SVM_vmcb01_pa (SVM_vmcb01 + KVM_VMCB_pa)
+
.section .noinstr.text, "ax"
/**
@@ -55,6 +57,16 @@ SYM_FUNC_START(__svm_vcpu_run)
mov %_ASM_ARG1, %_ASM_DI
.endif
+ /*
+ * Use a single vmcb (vmcb01 because it's always valid) for
+ * context switching guest state via VMLOAD/VMSAVE, that way
+ * the state doesn't need to be copied between vmcb01 and
+ * vmcb02 when switching vmcbs for nested virtualization.
+ */
+ mov SVM_vmcb01_pa(%_ASM_DI), %_ASM_AX
+1: vmload %_ASM_AX
+2:
+
/* Get svm->current_vmcb->pa into RAX. */
mov SVM_current_vmcb(%_ASM_DI), %_ASM_AX
mov KVM_VMCB_pa(%_ASM_AX), %_ASM_AX
@@ -80,16 +92,11 @@ SYM_FUNC_START(__svm_vcpu_run)
/* Enter guest mode */
sti
-1: vmrun %_ASM_AX
-
-2: cli
-
-#ifdef CONFIG_RETPOLINE
- /* IMPORTANT: Stuff the RSB immediately after VM-Exit, before RET! */
- FILL_RETURN_BUFFER %_ASM_AX, RSB_CLEAR_LOOPS, X86_FEATURE_RETPOLINE
-#endif
+3: vmrun %_ASM_AX
+4:
+ cli
- /* "POP" @svm to RAX. */
+ /* Pop @svm to RAX while it's the only available register. */
pop %_ASM_AX
/* Save all guest registers. */
@@ -110,6 +117,18 @@ SYM_FUNC_START(__svm_vcpu_run)
mov %r15, VCPU_R15(%_ASM_AX)
#endif
+ /* @svm can stay in RDI from now on. */
+ mov %_ASM_AX, %_ASM_DI
+
+ mov SVM_vmcb01_pa(%_ASM_DI), %_ASM_AX
+5: vmsave %_ASM_AX
+6:
+
+#ifdef CONFIG_RETPOLINE
+ /* IMPORTANT: Stuff the RSB immediately after VM-Exit, before RET! */
+ FILL_RETURN_BUFFER %_ASM_AX, RSB_CLEAR_LOOPS, X86_FEATURE_RETPOLINE
+#endif
+
/*
* Mitigate RETBleed for AMD/Hygon Zen uarch. RET should be
* untrained as soon as we exit the VM and are back to the
@@ -159,11 +178,19 @@ SYM_FUNC_START(__svm_vcpu_run)
pop %_ASM_BP
RET
-3: cmpb $0, kvm_rebooting
+10: cmpb $0, kvm_rebooting
jne 2b
ud2
+30: cmpb $0, kvm_rebooting
+ jne 4b
+ ud2
+50: cmpb $0, kvm_rebooting
+ jne 6b
+ ud2
- _ASM_EXTABLE(1b, 3b)
+ _ASM_EXTABLE(1b, 10b)
+ _ASM_EXTABLE(3b, 30b)
+ _ASM_EXTABLE(5b, 50b)
SYM_FUNC_END(__svm_vcpu_run)
--
2.31.1
^ permalink raw reply related [flat|nested] 13+ messages in thread
* [PATCH v2 6/8] KVM: SVM: restore host save area from assembly
[not found] <20221108151532.1377783-1-pbonzini@redhat.com>
` (3 preceding siblings ...)
2022-11-08 15:15 ` [PATCH v2 5/8] KVM: SVM: move guest vmsave/vmload to assembly Paolo Bonzini
@ 2022-11-08 15:15 ` Paolo Bonzini
2022-11-08 15:15 ` [PATCH v2 7/8] KVM: SVM: move MSR_IA32_SPEC_CTRL save/restore to assembly Paolo Bonzini
5 siblings, 0 replies; 13+ messages in thread
From: Paolo Bonzini @ 2022-11-08 15:15 UTC (permalink / raw)
To: linux-kernel, kvm
Cc: nathan, thomas.lendacky, andrew.cooper3, peterz, jmattson,
seanjc, stable
This is needed so that FILL_RETURN_BUFFER has access to the
percpu area via the GS segment base.
Cc: stable@vger.kernel.org
Fixes: f14eec0a3203 ("KVM: SVM: move more vmentry code to assembly")
Reported-by: Nathan Chancellor <nathan@kernel.org>
Analyzed-by: Andrew Cooper <andrew.cooper3@citrix.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
arch/x86/kvm/svm/svm.c | 3 +--
arch/x86/kvm/svm/svm.h | 2 +-
arch/x86/kvm/svm/svm_ops.h | 5 -----
arch/x86/kvm/svm/vmenter.S | 13 +++++++++++++
4 files changed, 15 insertions(+), 8 deletions(-)
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 0ba4feb19cb6..e15f6ea9e5cc 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -3922,8 +3922,7 @@ static noinstr void svm_vcpu_enter_exit(struct kvm_vcpu *vcpu)
} else {
struct svm_cpu_data *sd = per_cpu(svm_data, vcpu->cpu);
- __svm_vcpu_run(svm);
- vmload(__sme_page_pa(sd->save_area));
+ __svm_vcpu_run(svm, __sme_page_pa(sd->save_area));
}
guest_state_exit_irqoff();
diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
index 7ff1879e73c5..932f26be5675 100644
--- a/arch/x86/kvm/svm/svm.h
+++ b/arch/x86/kvm/svm/svm.h
@@ -684,6 +684,6 @@ void sev_es_unmap_ghcb(struct vcpu_svm *svm);
/* vmenter.S */
void __svm_sev_es_vcpu_run(struct vcpu_svm *svm);
-void __svm_vcpu_run(struct vcpu_svm *svm);
+void __svm_vcpu_run(struct vcpu_svm *svm, unsigned long hsave_pa);
#endif
diff --git a/arch/x86/kvm/svm/svm_ops.h b/arch/x86/kvm/svm/svm_ops.h
index 9430d6437c9f..36c8af87a707 100644
--- a/arch/x86/kvm/svm/svm_ops.h
+++ b/arch/x86/kvm/svm/svm_ops.h
@@ -61,9 +61,4 @@ static __always_inline void vmsave(unsigned long pa)
svm_asm1(vmsave, "a" (pa), "memory");
}
-static __always_inline void vmload(unsigned long pa)
-{
- svm_asm1(vmload, "a" (pa), "memory");
-}
-
#endif /* __KVM_X86_SVM_OPS_H */
diff --git a/arch/x86/kvm/svm/vmenter.S b/arch/x86/kvm/svm/vmenter.S
index 5bc2ed7d79c0..0a4272faf80f 100644
--- a/arch/x86/kvm/svm/vmenter.S
+++ b/arch/x86/kvm/svm/vmenter.S
@@ -35,6 +35,7 @@
/**
* __svm_vcpu_run - Run a vCPU via a transition to SVM guest mode
* @svm: struct vcpu_svm *
+ * @hsave_pa: unsigned long
*/
SYM_FUNC_START(__svm_vcpu_run)
push %_ASM_BP
@@ -49,6 +50,9 @@ SYM_FUNC_START(__svm_vcpu_run)
#endif
push %_ASM_BX
+ /* @hsave_pa is needed last after vmexit, save it first. */
+ push %_ASM_ARG2
+
/* Save @svm. */
push %_ASM_ARG1
@@ -124,6 +128,11 @@ SYM_FUNC_START(__svm_vcpu_run)
5: vmsave %_ASM_AX
6:
+ /* Pop @hsave_pa and restore GSBASE, allowing access to percpu data. */
+ pop %_ASM_AX
+7: vmload %_ASM_AX
+8:
+
#ifdef CONFIG_RETPOLINE
/* IMPORTANT: Stuff the RSB immediately after VM-Exit, before RET! */
FILL_RETURN_BUFFER %_ASM_AX, RSB_CLEAR_LOOPS, X86_FEATURE_RETPOLINE
@@ -187,10 +196,14 @@ SYM_FUNC_START(__svm_vcpu_run)
50: cmpb $0, kvm_rebooting
jne 6b
ud2
+70: cmpb $0, kvm_rebooting
+ jne 8b
+ ud2
_ASM_EXTABLE(1b, 10b)
_ASM_EXTABLE(3b, 30b)
_ASM_EXTABLE(5b, 50b)
+ _ASM_EXTABLE(7b, 70b)
SYM_FUNC_END(__svm_vcpu_run)
--
2.31.1
^ permalink raw reply related [flat|nested] 13+ messages in thread
* [PATCH v2 7/8] KVM: SVM: move MSR_IA32_SPEC_CTRL save/restore to assembly
[not found] <20221108151532.1377783-1-pbonzini@redhat.com>
` (4 preceding siblings ...)
2022-11-08 15:15 ` [PATCH v2 6/8] KVM: SVM: restore host save area from assembly Paolo Bonzini
@ 2022-11-08 15:15 ` Paolo Bonzini
2022-11-09 1:14 ` Sean Christopherson
5 siblings, 1 reply; 13+ messages in thread
From: Paolo Bonzini @ 2022-11-08 15:15 UTC (permalink / raw)
To: linux-kernel, kvm
Cc: nathan, thomas.lendacky, andrew.cooper3, peterz, jmattson,
seanjc, stable
Restoration of the host IA32_SPEC_CTRL value is probably too late
with respect to the return thunk training sequence.
With respect to the user/kernel boundary, AMD says, "If software chooses
to toggle STIBP (e.g., set STIBP on kernel entry, and clear it on kernel
exit), software should set STIBP to 1 before executing the return thunk
training sequence." I assume the same requirements apply to the guest/host
boundary. The return thunk training sequence is in vmenter.S, quite close
to the VM-exit. On hosts without V_SPEC_CTRL, however, the host's
IA32_SPEC_CTRL value is not restored until much later.
To avoid this, move the restoration of host SPEC_CTRL to assembly and,
for consistency, move the restoration of the guest SPEC_CTRL as well.
This is not particularly difficult, apart from some care to cover both
32- and 64-bit, and to share code between SEV-ES and normal vmentry.
Cc: stable@vger.kernel.org
Fixes: a149180fbcf3 ("x86: Add magic AMD return-thunk")
Suggested-by: Jim Mattson <jmattson@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
arch/x86/kernel/cpu/bugs.c | 13 +----
arch/x86/kvm/kvm-asm-offsets.c | 1 +
arch/x86/kvm/svm/svm.c | 38 +++++-------
arch/x86/kvm/svm/svm.h | 4 +-
arch/x86/kvm/svm/vmenter.S | 102 ++++++++++++++++++++++++++++++++-
5 files changed, 121 insertions(+), 37 deletions(-)
diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c
index da7c361f47e0..6ec0b7ce7453 100644
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -196,22 +196,15 @@ void __init check_bugs(void)
}
/*
- * NOTE: This function is *only* called for SVM. VMX spec_ctrl handling is
- * done in vmenter.S.
+ * NOTE: This function is *only* called for SVM, since Intel uses
+ * MSR_IA32_SPEC_CTRL for SSBD.
*/
void
x86_virt_spec_ctrl(u64 guest_spec_ctrl, u64 guest_virt_spec_ctrl, bool setguest)
{
- u64 msrval, guestval = guest_spec_ctrl, hostval = spec_ctrl_current();
+ u64 guestval, hostval;
struct thread_info *ti = current_thread_info();
- if (static_cpu_has(X86_FEATURE_MSR_SPEC_CTRL)) {
- if (hostval != guestval) {
- msrval = setguest ? guestval : hostval;
- wrmsrl(MSR_IA32_SPEC_CTRL, msrval);
- }
- }
-
/*
* If SSBD is not handled in MSR_SPEC_CTRL on AMD, update
* MSR_AMD64_L2_CFG or MSR_VIRT_SPEC_CTRL if supported.
diff --git a/arch/x86/kvm/kvm-asm-offsets.c b/arch/x86/kvm/kvm-asm-offsets.c
index f83e88b85bf2..b2877c2c8df1 100644
--- a/arch/x86/kvm/kvm-asm-offsets.c
+++ b/arch/x86/kvm/kvm-asm-offsets.c
@@ -16,6 +16,7 @@ static void __used common(void)
BLANK();
OFFSET(SVM_vcpu_arch_regs, vcpu_svm, vcpu.arch.regs);
OFFSET(SVM_current_vmcb, vcpu_svm, current_vmcb);
+ OFFSET(SVM_spec_ctrl, vcpu_svm, spec_ctrl);
OFFSET(SVM_vmcb01, vcpu_svm, vmcb01);
OFFSET(KVM_VMCB_pa, kvm_vmcb_info, pa);
}
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index e15f6ea9e5cc..512bc06a4ba1 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -730,6 +730,15 @@ static bool msr_write_intercepted(struct kvm_vcpu *vcpu, u32 msr)
u32 offset;
u32 *msrpm;
+ /*
+ * For non-nested case:
+ * If the L01 MSR bitmap does not intercept the MSR, then we need to
+ * save it.
+ *
+ * For nested case:
+ * If the L02 MSR bitmap does not intercept the MSR, then we need to
+ * save it.
+ */
msrpm = is_guest_mode(vcpu) ? to_svm(vcpu)->nested.msrpm:
to_svm(vcpu)->msrpm;
@@ -3911,18 +3920,19 @@ static fastpath_t svm_exit_handlers_fastpath(struct kvm_vcpu *vcpu)
return EXIT_FASTPATH_NONE;
}
-static noinstr void svm_vcpu_enter_exit(struct kvm_vcpu *vcpu)
+static noinstr void svm_vcpu_enter_exit(struct kvm_vcpu *vcpu, bool spec_ctrl_intercepted)
{
struct vcpu_svm *svm = to_svm(vcpu);
guest_state_enter_irqoff();
if (sev_es_guest(vcpu->kvm)) {
- __svm_sev_es_vcpu_run(svm);
+ __svm_sev_es_vcpu_run(svm, spec_ctrl_intercepted);
} else {
struct svm_cpu_data *sd = per_cpu(svm_data, vcpu->cpu);
- __svm_vcpu_run(svm, __sme_page_pa(sd->save_area));
+ __svm_vcpu_run(svm, __sme_page_pa(sd->save_area),
+ spec_ctrl_intercepted);
}
guest_state_exit_irqoff();
@@ -3931,6 +3941,7 @@ static noinstr void svm_vcpu_enter_exit(struct kvm_vcpu *vcpu)
static __no_kcsan fastpath_t svm_vcpu_run(struct kvm_vcpu *vcpu)
{
struct vcpu_svm *svm = to_svm(vcpu);
+ bool spec_ctrl_intercepted = msr_write_intercepted(vcpu, MSR_IA32_SPEC_CTRL);
trace_kvm_entry(vcpu);
@@ -3989,26 +4000,7 @@ static __no_kcsan fastpath_t svm_vcpu_run(struct kvm_vcpu *vcpu)
if (!static_cpu_has(X86_FEATURE_V_SPEC_CTRL))
x86_spec_ctrl_set_guest(svm->spec_ctrl, svm->virt_spec_ctrl);
- svm_vcpu_enter_exit(vcpu);
-
- /*
- * We do not use IBRS in the kernel. If this vCPU has used the
- * SPEC_CTRL MSR it may have left it on; save the value and
- * turn it off. This is much more efficient than blindly adding
- * it to the atomic save/restore list. Especially as the former
- * (Saving guest MSRs on vmexit) doesn't even exist in KVM.
- *
- * For non-nested case:
- * If the L01 MSR bitmap does not intercept the MSR, then we need to
- * save it.
- *
- * For nested case:
- * If the L02 MSR bitmap does not intercept the MSR, then we need to
- * save it.
- */
- if (!static_cpu_has(X86_FEATURE_V_SPEC_CTRL) &&
- unlikely(!msr_write_intercepted(vcpu, MSR_IA32_SPEC_CTRL)))
- svm->spec_ctrl = native_read_msr(MSR_IA32_SPEC_CTRL);
+ svm_vcpu_enter_exit(vcpu, spec_ctrl_intercepted);
if (!sev_es_guest(vcpu->kvm))
reload_tss(vcpu);
diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
index 932f26be5675..bf9ff39dc420 100644
--- a/arch/x86/kvm/svm/svm.h
+++ b/arch/x86/kvm/svm/svm.h
@@ -683,7 +683,7 @@ void sev_es_unmap_ghcb(struct vcpu_svm *svm);
/* vmenter.S */
-void __svm_sev_es_vcpu_run(struct vcpu_svm *svm);
-void __svm_vcpu_run(struct vcpu_svm *svm, unsigned long hsave_pa);
+void __svm_sev_es_vcpu_run(struct vcpu_svm *svm, bool spec_ctrl_intercepted);
+void __svm_vcpu_run(struct vcpu_svm *svm, unsigned long hsave_pa, bool spec_ctrl_intercepted);
#endif
diff --git a/arch/x86/kvm/svm/vmenter.S b/arch/x86/kvm/svm/vmenter.S
index 0a4272faf80f..a02eef724379 100644
--- a/arch/x86/kvm/svm/vmenter.S
+++ b/arch/x86/kvm/svm/vmenter.S
@@ -32,10 +32,70 @@
.section .noinstr.text, "ax"
+.macro RESTORE_GUEST_SPEC_CTRL
+ /* No need to do anything if SPEC_CTRL is unset or V_SPEC_CTRL is set */
+ ALTERNATIVE_2 "", \
+ "jmp 800f", X86_FEATURE_MSR_SPEC_CTRL, \
+ "", X86_FEATURE_V_SPEC_CTRL
+801:
+.endm
+
+.macro RESTORE_HOST_SPEC_CTRL
+ /* No need to do anything if SPEC_CTRL is unset or V_SPEC_CTRL is set */
+ ALTERNATIVE_2 "", \
+ "jmp 900f", X86_FEATURE_MSR_SPEC_CTRL, \
+ "", X86_FEATURE_V_SPEC_CTRL
+901:
+.endm
+
+.macro RESTORE_SPEC_CTRL_BODY
+800:
+ /*
+ * SPEC_CTRL handling: if the guest's SPEC_CTRL value differs from the
+ * host's, write the MSR. This is kept out-of-line so that the common
+ * case does not have to jump.
+ *
+ * IMPORTANT: To avoid RSB underflow attacks and any other nastiness,
+ * there must not be any returns or indirect branches between this code
+ * and vmentry.
+ */
+ movl SVM_spec_ctrl(%_ASM_DI), %eax
+ cmp PER_CPU_VAR(x86_spec_ctrl_current), %eax
+ je 801b
+ mov $MSR_IA32_SPEC_CTRL, %ecx
+ xor %edx, %edx
+ wrmsr
+ jmp 801b
+
+900:
+ /* Same for after vmexit. */
+ mov $MSR_IA32_SPEC_CTRL, %ecx
+
+ /*
+ * Load the value that the guest had written into MSR_IA32_SPEC_CTRL,
+ * if it was not intercepted during guest execution.
+ */
+ cmpb $0, (%_ASM_SP)
+ jnz 998f
+ rdmsr
+ movl %eax, SVM_spec_ctrl(%_ASM_DI)
+998:
+
+ /* Now restore the host value of the MSR if different from the guest's. */
+ movl PER_CPU_VAR(x86_spec_ctrl_current), %eax
+ cmp SVM_spec_ctrl(%_ASM_DI), %eax
+ je 901b
+ xor %edx, %edx
+ wrmsr
+ jmp 901b
+.endm
+
+
/**
* __svm_vcpu_run - Run a vCPU via a transition to SVM guest mode
* @svm: struct vcpu_svm *
* @hsave_pa: unsigned long
+ * @spec_ctrl_intercepted: bool
*/
SYM_FUNC_START(__svm_vcpu_run)
push %_ASM_BP
@@ -50,7 +110,12 @@ SYM_FUNC_START(__svm_vcpu_run)
#endif
push %_ASM_BX
- /* @hsave_pa is needed last after vmexit, save it first. */
+ /*
+ * Both @spec_ctrl_intercepted and @hsave_pa are used only after vmexit.
+ * @spec_ctrl_intercepted is needed later and accessed directly from
+ * the stack in RESTORE_HOST_SPEC_CTRL, so save it first.
+ */
+ push %_ASM_ARG3
push %_ASM_ARG2
/* Save @svm. */
@@ -61,6 +126,8 @@ SYM_FUNC_START(__svm_vcpu_run)
mov %_ASM_ARG1, %_ASM_DI
.endif
+ RESTORE_GUEST_SPEC_CTRL
+
/*
* Use a single vmcb (vmcb01 because it's always valid) for
* context switching guest state via VMLOAD/VMSAVE, that way
@@ -138,6 +205,8 @@ SYM_FUNC_START(__svm_vcpu_run)
FILL_RETURN_BUFFER %_ASM_AX, RSB_CLEAR_LOOPS, X86_FEATURE_RETPOLINE
#endif
+ RESTORE_HOST_SPEC_CTRL
+
/*
* Mitigate RETBleed for AMD/Hygon Zen uarch. RET should be
* untrained as soon as we exit the VM and are back to the
@@ -173,6 +242,9 @@ SYM_FUNC_START(__svm_vcpu_run)
xor %r15d, %r15d
#endif
+ /* "Pop" @spec_ctrl_intercepted. */
+ pop %_ASM_BX
+
pop %_ASM_BX
#ifdef CONFIG_X86_64
@@ -187,6 +259,8 @@ SYM_FUNC_START(__svm_vcpu_run)
pop %_ASM_BP
RET
+ RESTORE_SPEC_CTRL_BODY
+
10: cmpb $0, kvm_rebooting
jne 2b
ud2
@@ -210,6 +284,7 @@ SYM_FUNC_END(__svm_vcpu_run)
/**
* __svm_sev_es_vcpu_run - Run a SEV-ES vCPU via a transition to SVM guest mode
* @svm: struct vcpu_svm *
+ * @spec_ctrl_intercepted: bool
*/
SYM_FUNC_START(__svm_sev_es_vcpu_run)
push %_ASM_BP
@@ -224,8 +299,21 @@ SYM_FUNC_START(__svm_sev_es_vcpu_run)
#endif
push %_ASM_BX
+ /* Save @spec_ctrl_intercepted for RESTORE_HOST_SPEC_CTRL. */
+ push %_ASM_ARG2
+
+ /* Save @svm. */
+ push %_ASM_ARG1
+
+.ifnc _ASM_ARG1, _ASM_DI
+ /* Move @svm to RDI for RESTORE_GUEST_SPEC_CTRL. */
+ mov %_ASM_ARG1, %_ASM_DI
+.endif
+
+ RESTORE_GUEST_SPEC_CTRL
+
/* Get svm->current_vmcb->pa into RAX. */
- mov SVM_current_vmcb(%_ASM_ARG1), %_ASM_AX
+ mov SVM_current_vmcb(%_ASM_DI), %_ASM_AX
mov KVM_VMCB_pa(%_ASM_AX), %_ASM_AX
/* Enter guest mode */
@@ -235,11 +323,16 @@ SYM_FUNC_START(__svm_sev_es_vcpu_run)
2: cli
+ /* Pop @svm to RDI, guest registers have been saved already. */
+ pop %_ASM_DI
+
#ifdef CONFIG_RETPOLINE
/* IMPORTANT: Stuff the RSB immediately after VM-Exit, before RET! */
FILL_RETURN_BUFFER %_ASM_AX, RSB_CLEAR_LOOPS, X86_FEATURE_RETPOLINE
#endif
+ RESTORE_HOST_SPEC_CTRL
+
/*
* Mitigate RETBleed for AMD/Hygon Zen uarch. RET should be
* untrained as soon as we exit the VM and are back to the
@@ -249,6 +342,9 @@ SYM_FUNC_START(__svm_sev_es_vcpu_run)
*/
UNTRAIN_RET
+ /* "Pop" @spec_ctrl_intercepted. */
+ pop %_ASM_BX
+
pop %_ASM_BX
#ifdef CONFIG_X86_64
@@ -263,6 +359,8 @@ SYM_FUNC_START(__svm_sev_es_vcpu_run)
pop %_ASM_BP
RET
+ RESTORE_SPEC_CTRL_BODY
+
3: cmpb $0, kvm_rebooting
jne 2b
ud2
--
2.31.1
^ permalink raw reply related [flat|nested] 13+ messages in thread
* Re: [PATCH v2 2/8] KVM: SVM: replace regs argument of __svm_vcpu_run with vcpu_svm
2022-11-08 15:15 ` [PATCH v2 2/8] KVM: SVM: replace regs argument of __svm_vcpu_run with vcpu_svm Paolo Bonzini
@ 2022-11-08 20:54 ` Sean Christopherson
2022-11-09 10:35 ` Paolo Bonzini
0 siblings, 1 reply; 13+ messages in thread
From: Sean Christopherson @ 2022-11-08 20:54 UTC (permalink / raw)
To: Paolo Bonzini
Cc: linux-kernel, kvm, nathan, thomas.lendacky, andrew.cooper3,
peterz, jmattson, stable
On Tue, Nov 08, 2022, Paolo Bonzini wrote:
> Since registers are reachable through vcpu_svm, and we will
> need to access more fields of that struct, pass it instead
> of the regs[] array.
>
> No functional change intended.
>
> Cc: stable@vger.kernel.org
> Fixes: f14eec0a3203 ("KVM: SVM: move more vmentry code to assembly")
I don't think a Fixes: tag for a pure nop patch is fair to the original commit.
^ permalink raw reply [flat|nested] 13+ messages in thread
* Re: [PATCH v2 3/8] KVM: SVM: adjust register allocation for __svm_vcpu_run
2022-11-08 15:15 ` [PATCH v2 3/8] KVM: SVM: adjust register allocation for __svm_vcpu_run Paolo Bonzini
@ 2022-11-08 20:55 ` Sean Christopherson
0 siblings, 0 replies; 13+ messages in thread
From: Sean Christopherson @ 2022-11-08 20:55 UTC (permalink / raw)
To: Paolo Bonzini
Cc: linux-kernel, kvm, nathan, thomas.lendacky, andrew.cooper3,
peterz, jmattson, stable
On Tue, Nov 08, 2022, Paolo Bonzini wrote:
> In preparation for moving vmload/vmsave to __svm_vcpu_run,
> keep the pointer to the struct vcpu_svm in %rdi. This way
> it is possible to load svm->vmcb01.pa in %rax without
> clobbering the pointer to svm itself.
>
> No functional change intended.
>
> Cc: stable@vger.kernel.org
> Fixes: f14eec0a3203 ("KVM: SVM: move more vmentry code to assembly")
Same nit, Fixes: shouldn't be provided.
^ permalink raw reply [flat|nested] 13+ messages in thread
* Re: [PATCH v2 4/8] KVM: SVM: retrieve VMCB from assembly
2022-11-08 15:15 ` [PATCH v2 4/8] KVM: SVM: retrieve VMCB from assembly Paolo Bonzini
@ 2022-11-09 0:53 ` Sean Christopherson
2022-11-09 9:09 ` Paolo Bonzini
0 siblings, 1 reply; 13+ messages in thread
From: Sean Christopherson @ 2022-11-09 0:53 UTC (permalink / raw)
To: Paolo Bonzini
Cc: linux-kernel, kvm, nathan, thomas.lendacky, andrew.cooper3,
peterz, jmattson, stable
[-- Attachment #1: Type: text/plain, Size: 3005 bytes --]
On Tue, Nov 08, 2022, Paolo Bonzini wrote:
> This is needed in order to keep the number of arguments to 3 or less,
> after adding hsave_pa and spec_ctrl_intercepted. 32-bit builds only
> support passing three arguments in registers, fortunately all other
> data is reachable from the vcpu_svm struct.
Is it actually a problem if parameters are passed on the stack? The assembly
code mostly creates a stack frame, i.e. %ebp can be used to pull values off the
stack.
I dont think it will matter in the end (more below), but hypothetically if we
ended up with
void __svm_vcpu_run(struct kvm_vcpu *vcpu, unsigned long vmcb_pa,
unsigned long gsave_pa, unsigned long hsave_pa,
bool spec_ctrl_intercepted);
then the asm prologue would be something like:
/*
* Save @vcpu, @gsave_pa, @hsave_pa, and @spec_ctrl_intercepted, all of
* which are needed after VM-Exit.
*/
push %_ASM_ARG1
push %_ASM_ARG3
#ifdef CONFIG_X86_64
push %_ASM_ARG4
push %_ASM_ARG5
#else
push %_ASM_ARG4_EBP(%ebp)
push %_ASM_ARG5_EBP(%ebp)
#endif
which is a few extra memory accesses, especially for 32-bit, but no one cares
about 32-bit and I highly doubt a few extra PUSH+POP instructions will be noticeable.
Threading in yesterday's conversation...
> > What about adding dedicated structs to hold the non-regs params for VM-Enter and
> > VMRUN? Grabbing stuff willy-nilly in the assembly code makes the flows difficult
> > to read as there's nothing in the C code that describes what fields are actually
> > used.
>
> What fields are actually used is (like with any other function)
> "potentially all, you'll have to read the source code and in fact you
> can just read asm-offsets.c instead". What I mean is, I cannot offhand
> see or remember what fields are touched by svm_prepare_switch_to_guest,
> why would __svm_vcpu_run be any different?
It's different because if it were a normal C function, it would simply take
@vcpu, and maybe @spec_ctrl_intercepted to shave cycles after CLGI. But because
it's assembly and doesn't have to_svm() readily available (among other restrictions),
__svm_vcpu_run() ends up taking a mishmash of parameters, which for me makes it
rather difficult to understand what to expect.
Oooh, and after much staring I realized that the address of the host save area
is passed in because grabbing it after VM-Exit can't work. That's subtle, and
passing it in isn't strictly necessary; there's no reason the assembly code can't
grab it and stash it on the stack.
What about killing a few birds with one stone? Move the host save area PA to
its own per-CPU variable, and then grab that from assembly as well. Then it's
a bit more obvious why the address needs to be saved on the stack across VMRUN,
and my whining about the prototype being funky goes away. __svm_vcpu_run() and
__svm_sev_es_vcpu_run() would have identical prototypes too.
Attached patches would slot in early in the series. Tested SVM and SME-enabled
kernels, didn't test the SEV-ES bits.
[-- Attachment #2: 0001-KVM-SVM-Add-a-helper-to-convert-a-SME-aware-PA-back-.patch --]
[-- Type: text/x-diff, Size: 3055 bytes --]
From 59a4b14ec509e30e614beaa20ceb920c181e3739 Mon Sep 17 00:00:00 2001
From: Sean Christopherson <seanjc@google.com>
Date: Tue, 8 Nov 2022 15:25:41 -0800
Subject: [PATCH 1/2] KVM: SVM: Add a helper to convert a SME-aware PA back to
a struct page
Add __sme_pa_to_page() to pair with __sme_page_pa() and use it to replace
open coded equivalents, including for "iopm_base", which previously
avoided having to do __sme_clr() by storing the raw PA in the global
variable.
Opportunistically convert __sme_page_pa() to a helper to provide type
safety.
No functional change intended.
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
arch/x86/kvm/svm/svm.c | 9 ++++-----
arch/x86/kvm/svm/svm.h | 16 +++++++++++++++-
2 files changed, 19 insertions(+), 6 deletions(-)
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 58f0077d9357..bb7427fd1242 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -1065,8 +1065,7 @@ static void svm_hardware_unsetup(void)
for_each_possible_cpu(cpu)
svm_cpu_uninit(cpu);
- __free_pages(pfn_to_page(iopm_base >> PAGE_SHIFT),
- get_order(IOPM_SIZE));
+ __free_pages(__sme_pa_to_page(iopm_base), get_order(IOPM_SIZE));
iopm_base = 0;
}
@@ -1243,7 +1242,7 @@ static void init_vmcb(struct kvm_vcpu *vcpu)
if (!kvm_hlt_in_guest(vcpu->kvm))
svm_set_intercept(svm, INTERCEPT_HLT);
- control->iopm_base_pa = __sme_set(iopm_base);
+ control->iopm_base_pa = iopm_base;
control->msrpm_base_pa = __sme_set(__pa(svm->msrpm));
control->int_ctl = V_INTR_MASKING_MASK;
@@ -1443,7 +1442,7 @@ static void svm_vcpu_free(struct kvm_vcpu *vcpu)
sev_free_vcpu(vcpu);
- __free_page(pfn_to_page(__sme_clr(svm->vmcb01.pa) >> PAGE_SHIFT));
+ __free_page(__sme_pa_to_page(svm->vmcb01.pa));
__free_pages(virt_to_page(svm->msrpm), get_order(MSRPM_SIZE));
}
@@ -4970,7 +4969,7 @@ static __init int svm_hardware_setup(void)
iopm_va = page_address(iopm_pages);
memset(iopm_va, 0xff, PAGE_SIZE * (1 << order));
- iopm_base = page_to_pfn(iopm_pages) << PAGE_SHIFT;
+ iopm_base = __sme_page_pa(iopm_pages);
init_msrpm_offsets();
diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
index 6a7686bf6900..9a2567803006 100644
--- a/arch/x86/kvm/svm/svm.h
+++ b/arch/x86/kvm/svm/svm.h
@@ -24,7 +24,21 @@
#include "kvm_cache_regs.h"
-#define __sme_page_pa(x) __sme_set(page_to_pfn(x) << PAGE_SHIFT)
+/*
+ * Helpers to convert to/from physical addresses for pages whose address is
+ * consumed directly by hardware. Even though it's a physical address, SVM
+ * often restricts the address to the natural width, hence 'unsigned long'
+ * instead of 'hpa_t'.
+ */
+static inline unsigned long __sme_page_pa(struct page *page)
+{
+ return __sme_set(page_to_pfn(page) << PAGE_SHIFT);
+}
+
+static inline struct page *__sme_pa_to_page(unsigned long pa)
+{
+ return pfn_to_page(__sme_clr(pa) >> PAGE_SHIFT);
+}
#define IOPM_SIZE PAGE_SIZE * 3
#define MSRPM_SIZE PAGE_SIZE * 2
base-commit: 88cd4a037496682f164e7ae8dac13cd4ec8edc2b
--
2.38.1.431.g37b22c650d-goog
[-- Attachment #3: 0002-KVM-SVM-Snapshot-host-save-area-PA-in-dedicated-per-.patch --]
[-- Type: text/x-diff, Size: 4804 bytes --]
From e9a4f9af27d7d384dc36ad66a9856f9decb8ce02 Mon Sep 17 00:00:00 2001
From: Sean Christopherson <seanjc@google.com>
Date: Tue, 8 Nov 2022 15:32:58 -0800
Subject: [PATCH 2/2] KVM: SVM: Snapshot host save area PA in dedicated per-CPU
variable
Track the SME-aware physical address of the host save area outside of
"struct svm_cpu_data" so that a future patch can easily reference the
address from assembly code.
The "overhead" of always allocating the per-CPU data is more or less
meaningless in the grand scheme. And when KVM AMD is built as a module,
it's actually more costly (by a single pointer) to dynamically allocate
the struct, as the per-CPU data is allocated only when the module is
loaded.
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
arch/x86/kvm/svm/svm.c | 30 ++++++++++++++++--------------
arch/x86/kvm/svm/svm.h | 2 +-
2 files changed, 17 insertions(+), 15 deletions(-)
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index bb7427fd1242..8fc02bef4f85 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -246,6 +246,7 @@ struct kvm_ldttss_desc {
} __attribute__((packed));
DEFINE_PER_CPU(struct svm_cpu_data *, svm_data);
+DEFINE_PER_CPU(unsigned long, svm_host_save_area_pa);
/*
* Only MSR_TSC_AUX is switched via the user return hook. EFER is switched via
@@ -597,7 +598,7 @@ static int svm_hardware_enable(void)
wrmsrl(MSR_EFER, efer | EFER_SVME);
- wrmsrl(MSR_VM_HSAVE_PA, __sme_page_pa(sd->save_area));
+ wrmsrl(MSR_VM_HSAVE_PA, per_cpu(svm_host_save_area_pa, me));
if (static_cpu_has(X86_FEATURE_TSCRATEMSR)) {
/*
@@ -653,12 +654,13 @@ static void svm_cpu_uninit(int cpu)
per_cpu(svm_data, cpu) = NULL;
kfree(sd->sev_vmcbs);
- __free_page(sd->save_area);
+ __free_page(__sme_pa_to_page(per_cpu(svm_host_save_area_pa, cpu)));
kfree(sd);
}
static int svm_cpu_init(int cpu)
{
+ struct page *host_save_area;
struct svm_cpu_data *sd;
int ret = -ENOMEM;
@@ -666,20 +668,20 @@ static int svm_cpu_init(int cpu)
if (!sd)
return ret;
sd->cpu = cpu;
- sd->save_area = alloc_page(GFP_KERNEL | __GFP_ZERO);
- if (!sd->save_area)
- goto free_cpu_data;
ret = sev_cpu_init(sd);
if (ret)
- goto free_save_area;
+ goto free_cpu_data;
+
+ host_save_area = alloc_page(GFP_KERNEL | __GFP_ZERO);
+ if (!host_save_area)
+ goto free_cpu_data;
per_cpu(svm_data, cpu) = sd;
+ per_cpu(svm_host_save_area_pa, cpu) = __sme_page_pa(host_save_area);
return 0;
-free_save_area:
- __free_page(sd->save_area);
free_cpu_data:
kfree(sd);
return ret;
@@ -1449,7 +1451,6 @@ static void svm_vcpu_free(struct kvm_vcpu *vcpu)
static void svm_prepare_switch_to_guest(struct kvm_vcpu *vcpu)
{
struct vcpu_svm *svm = to_svm(vcpu);
- struct svm_cpu_data *sd = per_cpu(svm_data, vcpu->cpu);
if (sev_es_guest(vcpu->kvm))
sev_es_unmap_ghcb(svm);
@@ -1461,10 +1462,13 @@ static void svm_prepare_switch_to_guest(struct kvm_vcpu *vcpu)
* Save additional host state that will be restored on VMEXIT (sev-es)
* or subsequent vmload of host save area.
*/
- vmsave(__sme_page_pa(sd->save_area));
+ vmsave(per_cpu(svm_host_save_area_pa, vcpu->cpu));
if (sev_es_guest(vcpu->kvm)) {
struct sev_es_save_area *hostsa;
- hostsa = (struct sev_es_save_area *)(page_address(sd->save_area) + 0x400);
+ struct page *hostsa_page;
+
+ hostsa_page = __sme_pa_to_page(per_cpu(svm_host_save_area_pa, vcpu->cpu));
+ hostsa = (struct sev_es_save_area *)(page_address(hostsa_page) + 0x400);
sev_es_prepare_switch_to_guest(hostsa);
}
@@ -3920,8 +3924,6 @@ static noinstr void svm_vcpu_enter_exit(struct kvm_vcpu *vcpu)
if (sev_es_guest(vcpu->kvm)) {
__svm_sev_es_vcpu_run(vmcb_pa);
} else {
- struct svm_cpu_data *sd = per_cpu(svm_data, vcpu->cpu);
-
/*
* Use a single vmcb (vmcb01 because it's always valid) for
* context switching guest state via VMLOAD/VMSAVE, that way
@@ -3932,7 +3934,7 @@ static noinstr void svm_vcpu_enter_exit(struct kvm_vcpu *vcpu)
__svm_vcpu_run(vmcb_pa, (unsigned long *)&vcpu->arch.regs);
vmsave(svm->vmcb01.pa);
- vmload(__sme_page_pa(sd->save_area));
+ vmload(per_cpu(svm_host_save_area_pa, vcpu->cpu));
}
guest_state_exit_irqoff();
diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
index 9a2567803006..d9ec8ea69a56 100644
--- a/arch/x86/kvm/svm/svm.h
+++ b/arch/x86/kvm/svm/svm.h
@@ -303,7 +303,6 @@ struct svm_cpu_data {
u32 min_asid;
struct kvm_ldttss_desc *tss_desc;
- struct page *save_area;
struct vmcb *current_vmcb;
/* index = sev_asid, value = vmcb pointer */
@@ -311,6 +310,7 @@ struct svm_cpu_data {
};
DECLARE_PER_CPU(struct svm_cpu_data *, svm_data);
+DECLARE_PER_CPU(unsigned long, svm_host_save_area_pa);
void recalc_intercepts(struct vcpu_svm *svm);
--
2.38.1.431.g37b22c650d-goog
^ permalink raw reply related [flat|nested] 13+ messages in thread
* Re: [PATCH v2 7/8] KVM: SVM: move MSR_IA32_SPEC_CTRL save/restore to assembly
2022-11-08 15:15 ` [PATCH v2 7/8] KVM: SVM: move MSR_IA32_SPEC_CTRL save/restore to assembly Paolo Bonzini
@ 2022-11-09 1:14 ` Sean Christopherson
2022-11-09 9:29 ` Paolo Bonzini
0 siblings, 1 reply; 13+ messages in thread
From: Sean Christopherson @ 2022-11-09 1:14 UTC (permalink / raw)
To: Paolo Bonzini
Cc: linux-kernel, kvm, nathan, thomas.lendacky, andrew.cooper3,
peterz, jmattson, stable
On Tue, Nov 08, 2022, Paolo Bonzini wrote:
> diff --git a/arch/x86/kvm/svm/vmenter.S b/arch/x86/kvm/svm/vmenter.S
> index 0a4272faf80f..a02eef724379 100644
> --- a/arch/x86/kvm/svm/vmenter.S
> +++ b/arch/x86/kvm/svm/vmenter.S
> @@ -32,10 +32,70 @@
>
> .section .noinstr.text, "ax"
>
> +.macro RESTORE_GUEST_SPEC_CTRL
> + /* No need to do anything if SPEC_CTRL is unset or V_SPEC_CTRL is set */
> + ALTERNATIVE_2 "", \
> + "jmp 800f", X86_FEATURE_MSR_SPEC_CTRL, \
> + "", X86_FEATURE_V_SPEC_CTRL
> +801:
> +.endm
> +
> +.macro RESTORE_HOST_SPEC_CTRL
> + /* No need to do anything if SPEC_CTRL is unset or V_SPEC_CTRL is set */
> + ALTERNATIVE_2 "", \
> + "jmp 900f", X86_FEATURE_MSR_SPEC_CTRL, \
> + "", X86_FEATURE_V_SPEC_CTRL
> +901:
> +.endm
> +
> +.macro RESTORE_SPEC_CTRL_BODY
Can we split these into separate macros? It's a bit more typing, but it's not
immediately obvious that these are two independent chunks (I was expecting a JMP
from the 800 section into the 900 section).
E.g. RESTORE_GUEST_SPEC_CTRL_BODY and RESTORE_HOST_SPEC_CTRL_BODY
> +800:
Ugh, the multiple users makes it somewhat ugly, but rather than arbitrary numbers,
what about using named labels to make it easier to understand the branches?
E.g.
---
arch/x86/kvm/svm/vmenter.S | 43 +++++++++++++++++++++-----------------
1 file changed, 24 insertions(+), 19 deletions(-)
diff --git a/arch/x86/kvm/svm/vmenter.S b/arch/x86/kvm/svm/vmenter.S
index a02eef724379..23fd7353f0d0 100644
--- a/arch/x86/kvm/svm/vmenter.S
+++ b/arch/x86/kvm/svm/vmenter.S
@@ -32,24 +32,24 @@
.section .noinstr.text, "ax"
-.macro RESTORE_GUEST_SPEC_CTRL
+.macro RESTORE_GUEST_SPEC_CTRL name
/* No need to do anything if SPEC_CTRL is unset or V_SPEC_CTRL is set */
ALTERNATIVE_2 "", \
- "jmp 800f", X86_FEATURE_MSR_SPEC_CTRL, \
+ "jmp .Lrestore_guest_spec_ctrl\name", X86_FEATURE_MSR_SPEC_CTRL, \
"", X86_FEATURE_V_SPEC_CTRL
-801:
+.Lpost_restore_guest_spec_ctrl\name:
.endm
-.macro RESTORE_HOST_SPEC_CTRL
+.macro RESTORE_HOST_SPEC_CTRL name
/* No need to do anything if SPEC_CTRL is unset or V_SPEC_CTRL is set */
ALTERNATIVE_2 "", \
- "jmp 900f", X86_FEATURE_MSR_SPEC_CTRL, \
+ "jmp .Lrestore_host_spec_ctrl\name", X86_FEATURE_MSR_SPEC_CTRL, \
"", X86_FEATURE_V_SPEC_CTRL
-901:
+.Lpost_restore_host_spec_ctrl\name:
.endm
-.macro RESTORE_SPEC_CTRL_BODY
-800:
+.macro RESTORE_GUEST_SPEC_CTRL_BODY name
+.Lrestore_guest_spec_ctrl\name:
/*
* SPEC_CTRL handling: if the guest's SPEC_CTRL value differs from the
* host's, write the MSR. This is kept out-of-line so that the common
@@ -61,13 +61,16 @@
*/
movl SVM_spec_ctrl(%_ASM_DI), %eax
cmp PER_CPU_VAR(x86_spec_ctrl_current), %eax
- je 801b
+ je .Lpost_restore_guest_spec_ctrl\name
+
mov $MSR_IA32_SPEC_CTRL, %ecx
xor %edx, %edx
wrmsr
- jmp 801b
+ jmp .Lpost_restore_guest_spec_ctrl\name
+.endm
-900:
+.macro RESTORE_HOST_SPEC_CTRL_BODY name
+.Lrestore_host_spec_ctrl\name:
/* Same for after vmexit. */
mov $MSR_IA32_SPEC_CTRL, %ecx
@@ -76,18 +79,18 @@
* if it was not intercepted during guest execution.
*/
cmpb $0, (%_ASM_SP)
- jnz 998f
+ jnz .Lskip_save_guest_spec_ctrl\name
rdmsr
movl %eax, SVM_spec_ctrl(%_ASM_DI)
-998:
+.Lskip_save_guest_spec_ctrl\name:
/* Now restore the host value of the MSR if different from the guest's. */
movl PER_CPU_VAR(x86_spec_ctrl_current), %eax
cmp SVM_spec_ctrl(%_ASM_DI), %eax
- je 901b
+ je .Lpost_restore_host_spec_ctrl\name
xor %edx, %edx
wrmsr
- jmp 901b
+ jmp .Lpost_restore_host_spec_ctrl\name
.endm
@@ -259,7 +262,8 @@ SYM_FUNC_START(__svm_vcpu_run)
pop %_ASM_BP
RET
- RESTORE_SPEC_CTRL_BODY
+ RESTORE_GUEST_SPEC_CTRL_BODY
+ RESTORE_HOST_SPEC_CTRL_BODY
10: cmpb $0, kvm_rebooting
jne 2b
@@ -310,7 +314,7 @@ SYM_FUNC_START(__svm_sev_es_vcpu_run)
mov %_ASM_ARG1, %_ASM_DI
.endif
- RESTORE_GUEST_SPEC_CTRL
+ RESTORE_GUEST_SPEC_CTRL sev_es
/* Get svm->current_vmcb->pa into RAX. */
mov SVM_current_vmcb(%_ASM_DI), %_ASM_AX
@@ -331,7 +335,7 @@ SYM_FUNC_START(__svm_sev_es_vcpu_run)
FILL_RETURN_BUFFER %_ASM_AX, RSB_CLEAR_LOOPS, X86_FEATURE_RETPOLINE
#endif
- RESTORE_HOST_SPEC_CTRL
+ RESTORE_HOST_SPEC_CTRL sev_es
/*
* Mitigate RETBleed for AMD/Hygon Zen uarch. RET should be
@@ -359,7 +363,8 @@ SYM_FUNC_START(__svm_sev_es_vcpu_run)
pop %_ASM_BP
RET
- RESTORE_SPEC_CTRL_BODY
+ RESTORE_GUEST_SPEC_CTRL_BODY sev_es
+ RESTORE_HOST_SPEC_CTRL_BODY sev_es
3: cmpb $0, kvm_rebooting
jne 2b
base-commit: 0b242ada175d97a556866c48c80310860f634579
--
> @@ -61,6 +126,8 @@ SYM_FUNC_START(__svm_vcpu_run)
> mov %_ASM_ARG1, %_ASM_DI
> .endif
>
Can you add a comment to all of these to call out that RAX, RCX, and RDX might
get clobbered? It's easy to overlook that detail, and it matters on 32-bit where
the arguments use RCX and RDX. And because the clobber is conditional, it wouldn't
be that hard for a bug to escape initial testing.
/* This might clobber RAX, RCX, and RDX! */
> + RESTORE_GUEST_SPEC_CTRL
^ permalink raw reply related [flat|nested] 13+ messages in thread
* Re: [PATCH v2 4/8] KVM: SVM: retrieve VMCB from assembly
2022-11-09 0:53 ` Sean Christopherson
@ 2022-11-09 9:09 ` Paolo Bonzini
0 siblings, 0 replies; 13+ messages in thread
From: Paolo Bonzini @ 2022-11-09 9:09 UTC (permalink / raw)
To: Sean Christopherson
Cc: linux-kernel, kvm, nathan, thomas.lendacky, andrew.cooper3,
peterz, jmattson, stable
On 11/9/22 01:53, Sean Christopherson wrote:
> On Tue, Nov 08, 2022, Paolo Bonzini wrote:
>> This is needed in order to keep the number of arguments to 3 or less,
>> after adding hsave_pa and spec_ctrl_intercepted. 32-bit builds only
>> support passing three arguments in registers, fortunately all other
>> data is reachable from the vcpu_svm struct.
>
> Is it actually a problem if parameters are passed on the stack? The assembly
> code mostly creates a stack frame, i.e. %ebp can be used to pull values off the
> stack.
It's not, but given how little love 32-bit KVM receives, I prefer to
stick to the subset of the ABI that is "equivalent" to 64-bit.
> no one cares about 32-bit and I highly doubt a few extra PUSH+POP
> instructions will be noticeable.
Same reasoning (no one cares about 32-bits), different conclusions...
>> What fields are actually used is (like with any other function)
>> "potentially all, you'll have to read the source code and in fact you
>> can just read asm-offsets.c instead". What I mean is, I cannot offhand
>> see or remember what fields are touched by svm_prepare_switch_to_guest,
>> why would __svm_vcpu_run be any different?
>
> It's different because if it were a normal C function, it would simply take
> @vcpu, and maybe @spec_ctrl_intercepted to shave cycles after CLGI.
Not just for that, but especially to avoid making
msr_write_intercepted() noinstr.
> But because
> it's assembly and doesn't have to_svm() readily available (among other restrictions),
> __svm_vcpu_run() ends up taking a mishmash of parameters, which for me makes it
> rather difficult to understand what to expect.
Yeah, there could be three reasons to have parameters in assembly:
* you just need them (@svm)
* it's too much of a pain to compute it in assembly
(@spec_ctrl_intercepted, @hsave_pa)
* it needs to be computed outside the clgi/stgi region (not happening
here, only mentioned for completeness)
As this patch shows, @vmcb is not much of a pain to compute in assembly:
it is just two instructions, and not passing it in simplifies register
allocation (the weird push/pop goes away) because all the arguments
except @svm/_ASM_ARG1 are needed only after vmexit.
> Oooh, and after much staring I realized that the address of the host save area
> is passed in because grabbing it after VM-Exit can't work. That's subtle, and
> passing it in isn't strictly necessary; there's no reason the assembly code can't
> grab it and stash it on the stack.
Right, in fact that's not the reason why it's passed in---it's just to
avoid coding page_to_pfn() in assembly, and to limit the differences
between the regular and SEV-ES cases. But using a per-CPU variable is
fine (either in addition to the struct page, which "wastes" 8 bytes per
CPU, or as a replacement).
> What about killing a few birds with one stone? Move the host save area PA to
> its own per-CPU variable, and then grab that from assembly as well.
I would still place it in struct svm_cpu_data itself, I'll see how it
looks and possibly post v3.
Paolo
^ permalink raw reply [flat|nested] 13+ messages in thread
* Re: [PATCH v2 7/8] KVM: SVM: move MSR_IA32_SPEC_CTRL save/restore to assembly
2022-11-09 1:14 ` Sean Christopherson
@ 2022-11-09 9:29 ` Paolo Bonzini
0 siblings, 0 replies; 13+ messages in thread
From: Paolo Bonzini @ 2022-11-09 9:29 UTC (permalink / raw)
To: Sean Christopherson
Cc: linux-kernel, kvm, nathan, thomas.lendacky, andrew.cooper3,
peterz, jmattson, stable
On 11/9/22 02:14, Sean Christopherson wrote:
>>
>> +.macro RESTORE_SPEC_CTRL_BODY
>
> Can we split these into separate macros? It's a bit more typing, but it's not
> immediately obvious that these are two independent chunks (I was expecting a JMP
> from the 800 section into the 900 section).
>
> E.g. RESTORE_GUEST_SPEC_CTRL_BODY and RESTORE_HOST_SPEC_CTRL_BODY
Sure, I had it like that in an earlier version. I didn't see much
benefit but it is indeed a bit more readable if you order the macros like
.macro RESTORE_GUEST_SPEC_CTRL
.macro RESTORE_GUEST_SPEC_CTRL_BODY
.macro RESTORE_HOST_SPEC_CTRL
.macro RESTORE_HOST_SPEC_CTRL_BODY
>> +800:
>
> Ugh, the multiple users makes it somewhat ugly, but rather than arbitrary numbers,
> what about using named labels to make it easier to understand the branches?
I think it's okay if we separate the macros.
Paolo
^ permalink raw reply [flat|nested] 13+ messages in thread
* Re: [PATCH v2 2/8] KVM: SVM: replace regs argument of __svm_vcpu_run with vcpu_svm
2022-11-08 20:54 ` Sean Christopherson
@ 2022-11-09 10:35 ` Paolo Bonzini
0 siblings, 0 replies; 13+ messages in thread
From: Paolo Bonzini @ 2022-11-09 10:35 UTC (permalink / raw)
To: Sean Christopherson
Cc: linux-kernel, kvm, nathan, thomas.lendacky, andrew.cooper3,
peterz, jmattson, stable
On 11/8/22 21:54, Sean Christopherson wrote:
> On Tue, Nov 08, 2022, Paolo Bonzini wrote:
>> Since registers are reachable through vcpu_svm, and we will
>> need to access more fields of that struct, pass it instead
>> of the regs[] array.
>>
>> No functional change intended.
>>
>> Cc: stable@vger.kernel.org
>> Fixes: f14eec0a3203 ("KVM: SVM: move more vmentry code to assembly")
>
> I don't think a Fixes: tag for a pure nop patch is fair to the original commit.
That's for the sake of correct tracking in stable@, still it's not the
right commit to point at:
- f14eec0a3203 did not move the RSB stuffing before the GSBASE restore,
the code before was:
vmexit_fill_RSB();
#ifdef CONFIG_X86_64
wrmsrl(MSR_GS_BASE, svm->host.gs_base);
#else
- anyway it wasn't really buggy at the time: it's only in -next that
FILL_RETURN_BUFFER uses percpu data, because alternatives take care of
the X86_FEATURE_* checks
The real reason to do all this is to access the percpu host spec_ctrl,
which in turn is needed for retbleed. I'll point the Fixes tag to
a149180fbcf3 ("x86: Add magic AMD return-thunk") instead, again just for
the sake of tracking releases that need the change to full fix retbleed.
Paolo
^ permalink raw reply [flat|nested] 13+ messages in thread
end of thread, other threads:[~2022-11-09 10:36 UTC | newest]
Thread overview: 13+ messages (download: mbox.gz / follow: Atom feed)
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2022-11-08 15:15 ` [PATCH v2 2/8] KVM: SVM: replace regs argument of __svm_vcpu_run with vcpu_svm Paolo Bonzini
2022-11-08 20:54 ` Sean Christopherson
2022-11-09 10:35 ` Paolo Bonzini
2022-11-08 15:15 ` [PATCH v2 3/8] KVM: SVM: adjust register allocation for __svm_vcpu_run Paolo Bonzini
2022-11-08 20:55 ` Sean Christopherson
2022-11-08 15:15 ` [PATCH v2 4/8] KVM: SVM: retrieve VMCB from assembly Paolo Bonzini
2022-11-09 0:53 ` Sean Christopherson
2022-11-09 9:09 ` Paolo Bonzini
2022-11-08 15:15 ` [PATCH v2 5/8] KVM: SVM: move guest vmsave/vmload to assembly Paolo Bonzini
2022-11-08 15:15 ` [PATCH v2 6/8] KVM: SVM: restore host save area from assembly Paolo Bonzini
2022-11-08 15:15 ` [PATCH v2 7/8] KVM: SVM: move MSR_IA32_SPEC_CTRL save/restore to assembly Paolo Bonzini
2022-11-09 1:14 ` Sean Christopherson
2022-11-09 9:29 ` Paolo Bonzini
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