[kvm-unit-tests PATCH v3 07/20] x86/svm: Don't VMLOAD/VMSAVE "guest" state around VMRUN

[Sean Christopherson <seanjc@google.com>]

Drop the completely asinine and *extremely* confusing VMLOAD and VMSAVE
usage around VMRUN, as loading and saving _just_ guest state is both
unnecessary and dangerous.  E.g. GS.base, which KUT uses for per-CPU data,
is handled by VMLOAD/VMSAVE, and so loading guest state before VMRUN
without loading host state after #VMEXIT is wildly broken.  The only
reason the code "works" is because all relevant host state is copied
verbatim into the guest's save area, i.e. the host and guest use the same
state.  Double-down on sharing state between host and guest as a proper
fix is much more involved and delicate, e.g. would require ensuring
GS.base is loaded with the host's value prior to swapping GPRs (which are
per-CPU).

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 x86/svm.h | 4 ----
 1 file changed, 4 deletions(-)

diff --git a/x86/svm.h b/x86/svm.h
index 4e7e9e7a..21b3ac99 100644
--- a/x86/svm.h
+++ b/x86/svm.h
@@ -435,7 +435,6 @@ static inline void clgi(void)
 }
 
 #define ASM_PRE_VMRUN_CMD                       \
-                "vmload %%rax\n\t"              \
                 "mov " GUEST_REG(rflags) ", %%r15\n\t" \
                 "mov %%r15, 0x170(%%rax)\n\t"   \
                 "mov " GUEST_REG(rax) ", %%r15\n\t" \
@@ -448,9 +447,6 @@ static inline void clgi(void)
                 "mov %%r15, " GUEST_REG(rflags) "\n\t" \
                 "mov 0x1f8(%%rax), %%r15\n\t"   \
                 "mov %%r15, " GUEST_REG(rax)"\n\t" \
-                "vmsave %%rax\n\t"              \
-
-
 
 #define SVM_BARE_VMRUN \
 	asm volatile ( \
-- 
2.54.0.563.g4f69b47b94-goog