diff mbox series

[v11,02/16] KVM: x86: Use a new flag for branch targets

Message ID 20230913124227.12574-3-binbin.wu@linux.intel.com (mailing list archive)
State New, archived
Headers show
Series LAM and LASS KVM Enabling | expand

Commit Message

Binbin Wu Sept. 13, 2023, 12:42 p.m. UTC 
Use the new flag X86EMUL_F_BRANCH instead of X86EMUL_F_FETCH in assign_eip()
to distinguish instruction fetch and branch target computation for features
that handle differently on them, e.g. Linear Address Space Separation (LASS).

As of this patch, X86EMUL_F_BRANCH and X86EMUL_F_FETCH are identical as far
as KVM is concerned.

No functional change intended.

Signed-off-by: Binbin Wu <binbin.wu@linux.intel.com>
Tested-by: Xuelian Guo <xuelian.guo@intel.com>
---
 arch/x86/kvm/emulate.c     | 5 +++--
 arch/x86/kvm/kvm_emulate.h | 1 +
 2 files changed, 4 insertions(+), 2 deletions(-)

Comments

Sean Christopherson Oct. 23, 2023, 4:20 p.m. UTC | #1 
On Wed, Sep 13, 2023, Binbin Wu wrote:
> Use the new flag X86EMUL_F_BRANCH instead of X86EMUL_F_FETCH in assign_eip()
> to distinguish instruction fetch and branch target computation for features
> that handle differently on them, e.g. Linear Address Space Separation (LASS).

A slightly different shortlog+changelog:

  KVM: x86: Add an emulator flag to differntiate branch targets from fetches

  Add an emulator flag, X86EMUL_F_BRANCH, and use it instead of
  X86EMUL_F_FETCH in assign_eip() to distinguish between instruction fetch
  and branch target computation for features that handle them differently,
  e.g. Intel's upcoming Linear Address Space Separation (LASS) applies to
  code fetches but not branch target calculations.

The shortlog in particular is far too vague.

> As of this patch, X86EMUL_F_BRANCH and X86EMUL_F_FETCH are identical as far
> as KVM is concerned.

This patch looks good, but I'm going to skip it for now as it's not needed until
LASS is supported, since LAM doesn't differentiate between the two.  I.e. this
should have been the first patch in the LASS portion of the series.  No need to
repost, it's trivially easy to tweak vmx_get_untagged_addr().
diff mbox series

Patch

diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index 87ee1802166a..274d6e7aa0c1 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -721,7 +721,8 @@  static __always_inline int __linearize(struct x86_emulate_ctxt *ctxt,
 		    (flags & X86EMUL_F_WRITE))
 			goto bad;
 		/* unreadable code segment */
-		if (!(flags & X86EMUL_F_FETCH) && (desc.type & 8) && !(desc.type & 2))
+		if (!(flags & (X86EMUL_F_FETCH | X86EMUL_F_BRANCH)) &&
+		    (desc.type & 8) && !(desc.type & 2))
 			goto bad;
 		lim = desc_limit_scaled(&desc);
 		if (!(desc.type & 8) && (desc.type & 4)) {
@@ -772,7 +773,7 @@  static inline int assign_eip(struct x86_emulate_ctxt *ctxt, ulong dst)
 	if (ctxt->op_bytes != sizeof(unsigned long))
 		addr.ea = dst & ((1UL << (ctxt->op_bytes << 3)) - 1);
 	rc = __linearize(ctxt, addr, &max_size, 1, ctxt->mode, &linear,
-			 X86EMUL_F_FETCH);
+			 X86EMUL_F_BRANCH);
 	if (rc == X86EMUL_CONTINUE)
 		ctxt->_eip = addr.ea;
 	return rc;
diff --git a/arch/x86/kvm/kvm_emulate.h b/arch/x86/kvm/kvm_emulate.h
index e24c8ac7b930..e1fd83908334 100644
--- a/arch/x86/kvm/kvm_emulate.h
+++ b/arch/x86/kvm/kvm_emulate.h
@@ -91,6 +91,7 @@  struct x86_instruction_info {
 /* x86-specific emulation flags */
 #define X86EMUL_F_WRITE			BIT(0)
 #define X86EMUL_F_FETCH			BIT(1)
+#define X86EMUL_F_BRANCH		BIT(2)
 
 struct x86_emulate_ops {
 	void (*vm_bugged)(struct x86_emulate_ctxt *ctxt);