[PATCH v6 13/48] KVM: PPC: Book3S 64: Move GUEST_MODE_SKIP test into KVM
Nicholas Piggin
npiggin at gmail.com
Mon Apr 5 11:19:13 AEST 2021
Move the GUEST_MODE_SKIP logic into KVM code. This is quite a KVM
internal detail that has no real need to be in common handlers.
Also add a comment explaining why this thing exists.
Reviewed-by: Daniel Axtens <dja at axtens.net>
Reviewed-by: Fabiano Rosas <farosas at linux.ibm.com>
Signed-off-by: Nicholas Piggin <npiggin at gmail.com>
---
arch/powerpc/kernel/exceptions-64s.S | 60 ----------------------------
arch/powerpc/kvm/book3s_64_entry.S | 59 ++++++++++++++++++++++++++-
2 files changed, 58 insertions(+), 61 deletions(-)
diff --git a/arch/powerpc/kernel/exceptions-64s.S b/arch/powerpc/kernel/exceptions-64s.S
index 162595af1ac7..16fbfde960e7 100644
--- a/arch/powerpc/kernel/exceptions-64s.S
+++ b/arch/powerpc/kernel/exceptions-64s.S
@@ -133,7 +133,6 @@ name:
#define IBRANCH_TO_COMMON .L_IBRANCH_TO_COMMON_\name\() /* ENTRY branch to common */
#define IREALMODE_COMMON .L_IREALMODE_COMMON_\name\() /* Common runs in realmode */
#define IMASK .L_IMASK_\name\() /* IRQ soft-mask bit */
-#define IKVM_SKIP .L_IKVM_SKIP_\name\() /* Generate KVM skip handler */
#define IKVM_REAL .L_IKVM_REAL_\name\() /* Real entry tests KVM */
#define __IKVM_REAL(name) .L_IKVM_REAL_ ## name
#define IKVM_VIRT .L_IKVM_VIRT_\name\() /* Virt entry tests KVM */
@@ -190,9 +189,6 @@ do_define_int n
.ifndef IMASK
IMASK=0
.endif
- .ifndef IKVM_SKIP
- IKVM_SKIP=0
- .endif
.ifndef IKVM_REAL
IKVM_REAL=0
.endif
@@ -250,15 +246,10 @@ do_define_int n
.balign IFETCH_ALIGN_BYTES
\name\()_kvm:
- .if IKVM_SKIP
- cmpwi r10,KVM_GUEST_MODE_SKIP
- beq 89f
- .else
BEGIN_FTR_SECTION
ld r10,IAREA+EX_CFAR(r13)
std r10,HSTATE_CFAR(r13)
END_FTR_SECTION_IFSET(CPU_FTR_CFAR)
- .endif
ld r10,IAREA+EX_CTR(r13)
mtctr r10
@@ -285,27 +276,6 @@ END_FTR_SECTION_IFSET(CPU_FTR_HAS_PPR)
ori r12,r12,(IVEC)
.endif
b kvmppc_interrupt
-
- .if IKVM_SKIP
-89: mtocrf 0x80,r9
- ld r10,IAREA+EX_CTR(r13)
- mtctr r10
- ld r9,IAREA+EX_R9(r13)
- ld r10,IAREA+EX_R10(r13)
- ld r11,IAREA+EX_R11(r13)
- ld r12,IAREA+EX_R12(r13)
- .if IHSRR_IF_HVMODE
- BEGIN_FTR_SECTION
- b kvmppc_skip_Hinterrupt
- FTR_SECTION_ELSE
- b kvmppc_skip_interrupt
- ALT_FTR_SECTION_END_IFSET(CPU_FTR_HVMODE | CPU_FTR_ARCH_206)
- .elseif IHSRR
- b kvmppc_skip_Hinterrupt
- .else
- b kvmppc_skip_interrupt
- .endif
- .endif
.endm
#else
@@ -1083,7 +1053,6 @@ INT_DEFINE_BEGIN(machine_check)
ISET_RI=0
IDAR=1
IDSISR=1
- IKVM_SKIP=1
IKVM_REAL=1
INT_DEFINE_END(machine_check)
@@ -1356,7 +1325,6 @@ INT_DEFINE_BEGIN(data_access)
IVEC=0x300
IDAR=1
IDSISR=1
- IKVM_SKIP=1
IKVM_REAL=1
INT_DEFINE_END(data_access)
@@ -1410,7 +1378,6 @@ ALT_MMU_FTR_SECTION_END_IFCLR(MMU_FTR_TYPE_RADIX)
INT_DEFINE_BEGIN(data_access_slb)
IVEC=0x380
IDAR=1
- IKVM_SKIP=1
IKVM_REAL=1
INT_DEFINE_END(data_access_slb)
@@ -2080,7 +2047,6 @@ INT_DEFINE_BEGIN(h_data_storage)
IHSRR=1
IDAR=1
IDSISR=1
- IKVM_SKIP=1
IKVM_REAL=1
IKVM_VIRT=1
INT_DEFINE_END(h_data_storage)
@@ -3024,32 +2990,6 @@ EXPORT_SYMBOL(do_uaccess_flush)
MASKED_INTERRUPT
MASKED_INTERRUPT hsrr=1
-#ifdef CONFIG_KVM_BOOK3S_64_HANDLER
-kvmppc_skip_interrupt:
- /*
- * Here all GPRs are unchanged from when the interrupt happened
- * except for r13, which is saved in SPRG_SCRATCH0.
- */
- mfspr r13, SPRN_SRR0
- addi r13, r13, 4
- mtspr SPRN_SRR0, r13
- GET_SCRATCH0(r13)
- RFI_TO_KERNEL
- b .
-
-kvmppc_skip_Hinterrupt:
- /*
- * Here all GPRs are unchanged from when the interrupt happened
- * except for r13, which is saved in SPRG_SCRATCH0.
- */
- mfspr r13, SPRN_HSRR0
- addi r13, r13, 4
- mtspr SPRN_HSRR0, r13
- GET_SCRATCH0(r13)
- HRFI_TO_KERNEL
- b .
-#endif
-
/*
* Relocation-on interrupts: A subset of the interrupts can be delivered
* with IR=1/DR=1, if AIL==2 and MSR.HV won't be changed by delivering
diff --git a/arch/powerpc/kvm/book3s_64_entry.S b/arch/powerpc/kvm/book3s_64_entry.S
index 7a039ea78f15..bf927e7a06af 100644
--- a/arch/powerpc/kvm/book3s_64_entry.S
+++ b/arch/powerpc/kvm/book3s_64_entry.S
@@ -1,6 +1,7 @@
/* SPDX-License-Identifier: GPL-2.0-only */
#include <asm/asm-offsets.h>
#include <asm/cache.h>
+#include <asm/exception-64s.h>
#include <asm/kvm_asm.h>
#include <asm/kvm_book3s_asm.h>
#include <asm/ppc_asm.h>
@@ -20,9 +21,12 @@ kvmppc_interrupt:
* guest R12 saved in shadow VCPU SCRATCH0
* guest R13 saved in SPRN_SCRATCH0
*/
-#ifdef CONFIG_KVM_BOOK3S_HV_POSSIBLE
std r9,HSTATE_SCRATCH2(r13)
lbz r9,HSTATE_IN_GUEST(r13)
+ cmpwi r9,KVM_GUEST_MODE_SKIP
+ beq- .Lmaybe_skip
+.Lno_skip:
+#ifdef CONFIG_KVM_BOOK3S_HV_POSSIBLE
cmpwi r9,KVM_GUEST_MODE_HOST_HV
beq kvmppc_bad_host_intr
#ifdef CONFIG_KVM_BOOK3S_PR_POSSIBLE
@@ -32,5 +36,58 @@ kvmppc_interrupt:
#endif
b kvmppc_interrupt_hv
#else
+ ld r9,HSTATE_SCRATCH2(r13)
b kvmppc_interrupt_pr
#endif
+
+/*
+ * "Skip" interrupts are part of a trick KVM uses a with hash guests to load
+ * the faulting instruction in guest memory from the the hypervisor without
+ * walking page tables.
+ *
+ * When the guest takes a fault that requires the hypervisor to load the
+ * instruction (e.g., MMIO emulation), KVM is running in real-mode with HV=1
+ * and the guest MMU context loaded. It sets KVM_GUEST_MODE_SKIP, and sets
+ * MSR[DR]=1 while leaving MSR[IR]=0, so it continues to fetch HV instructions
+ * but loads and stores will access the guest context. This is used to load
+ * the faulting instruction using the faulting guest effective address.
+ *
+ * However the guest context may not be able to translate, or it may cause a
+ * machine check or other issue, which results in a fault in the host
+ * (even with KVM-HV).
+ *
+ * These faults come here because KVM_GUEST_MODE_SKIP was set, so if they
+ * are (or are likely) caused by that load, the instruction is skipped by
+ * just returning with the PC advanced +4, where it is noticed the load did
+ * not execute and it goes to the slow path which walks the page tables to
+ * read guest memory.
+ */
+.Lmaybe_skip:
+ cmpwi r12,BOOK3S_INTERRUPT_MACHINE_CHECK
+ beq 1f
+ cmpwi r12,BOOK3S_INTERRUPT_DATA_STORAGE
+ beq 1f
+ cmpwi r12,BOOK3S_INTERRUPT_DATA_SEGMENT
+ beq 1f
+#ifdef CONFIG_KVM_BOOK3S_HV_POSSIBLE
+ /* HSRR interrupts get 2 added to interrupt number */
+ cmpwi r12,BOOK3S_INTERRUPT_H_DATA_STORAGE | 0x2
+ beq 2f
+#endif
+ b .Lno_skip
+1: mfspr r9,SPRN_SRR0
+ addi r9,r9,4
+ mtspr SPRN_SRR0,r9
+ ld r12,HSTATE_SCRATCH0(r13)
+ ld r9,HSTATE_SCRATCH2(r13)
+ GET_SCRATCH0(r13)
+ RFI_TO_KERNEL
+#ifdef CONFIG_KVM_BOOK3S_HV_POSSIBLE
+2: mfspr r9,SPRN_HSRR0
+ addi r9,r9,4
+ mtspr SPRN_HSRR0,r9
+ ld r12,HSTATE_SCRATCH0(r13)
+ ld r9,HSTATE_SCRATCH2(r13)
+ GET_SCRATCH0(r13)
+ HRFI_TO_KERNEL
+#endif
--
2.23.0
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