[RFC PATCH v6 92/92] kvm: x86: fallback to the single-step on multipage CMPXCHG emulation
From: Adalbert Lazăr <hidden>
Date: 2019-08-09 16:06:30
Also in:
kvm, linux-mm
Subsystem:
kernel virtual machine for x86 (kvm/x86), the rest, x86 architecture (32-bit and 64-bit) · Maintainers:
Sean Christopherson, Paolo Bonzini, Linus Torvalds, Thomas Gleixner, Ingo Molnar, Borislav Petkov, Dave Hansen
From: Mihai Donțu <redacted> There are cases where we need to emulate a CMPXCHG that touches two pages (4 in one and another 4 in the next, for example). Because it is not easy to map two pages in the kernel so that we can directly execute the exchange instruction, we fallback to single-stepping. Luckly, this is an uncommon occurrence making the overhead of the single-step mechanism acceptable. Signed-off-by: Mihai Donțu <redacted> Signed-off-by: Adalbert Lazăr <redacted> --- arch/x86/kvm/x86.c | 15 +++++++++------ 1 file changed, 9 insertions(+), 6 deletions(-)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 0e904782d303..e283b074db26 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c@@ -5671,6 +5671,12 @@ static int emulator_cmpxchg_emulated(struct x86_emulate_ctxt *ctxt, #define CMPXCHG_MAX_BYTES 8 #endif + gpa = kvm_mmu_gva_to_gpa_write(vcpu, addr, NULL); + + if (gpa == UNMAPPED_GVA || + (gpa & PAGE_MASK) == APIC_DEFAULT_PHYS_BASE) + goto emul_write; + /* guests cmpxchg{8,16}b have to be emulated atomically */ if (bytes > CMPXCHG_MAX_BYTES || (bytes & (bytes - 1))) goto emul_write;
@@ -5678,12 +5684,6 @@ static int emulator_cmpxchg_emulated(struct x86_emulate_ctxt *ctxt, if (bytes == 16 && !system_has_cmpxchg_double()) goto emul_write; - gpa = kvm_mmu_gva_to_gpa_write(vcpu, addr, NULL); - - if (gpa == UNMAPPED_GVA || - (gpa & PAGE_MASK) == APIC_DEFAULT_PHYS_BASE) - goto emul_write; - if (((gpa + bytes - 1) & PAGE_MASK) != (gpa & PAGE_MASK)) goto emul_write;
@@ -5772,6 +5772,9 @@ static int emulator_cmpxchg_emulated(struct x86_emulate_ctxt *ctxt, return X86EMUL_CONTINUE; emul_write: + if (kvmi_tracked_gfn(vcpu, gpa >> PAGE_SHIFT)) + return X86EMUL_UNHANDLEABLE; + printk_once(KERN_WARNING "kvm: emulating exchange as write\n"); return emulator_write_emulated(ctxt, addr, new, bytes, exception);
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