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KVM: SVM: Disable SEV-ES support if MMIO caching is disable

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Disable SEV-ES if MMIO caching is disabled as SEV-ES relies on MMIO SPTEs
generating #NPF(RSVD), which are reflected by the CPU into the guest as
a #VC.  With SEV-ES, the untrusted host, a.k.a. KVM, doesn't have access
to the guest instruction stream or register state and so can't directly
emulate in response to a #NPF on an emulated MMIO GPA.  Disabling MMIO
caching means guest accesses to emulated MMIO ranges cause #NPF(!PRESENT),
and those flavors of #NPF cause automatic VM-Exits, not #VC.

Adjust KVM's MMIO masks to account for the C-bit location prior to doing
SEV(-ES) setup, and document that dependency between adjusting the MMIO
SPTE mask and SEV(-ES) setup.

Fixes: b09763da4d ("KVM: x86/mmu: Add module param to disable MMIO caching (for testing)")
Reported-by: Michael Roth <michael.roth@amd.com>
Tested-by: Michael Roth <michael.roth@amd.com>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Cc: stable@vger.kernel.org
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20220803224957.1285926-4-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Sean Christopherson 2022-08-03 22:49:57 +00:00 committed by Paolo Bonzini
parent c3e0c8c2e8
commit 0c29397ac1
5 changed files with 19 additions and 5 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
arch/x86/kvm/mmu.h
View File

@ -6,6 +6,8 @@
#include "kvm_cache_regs.h"
#include "cpuid.h"
extern bool __read_mostly enable_mmio_caching;
#define PT_WRITABLE_SHIFT 1
#define PT_USER_SHIFT 2

1
arch/x86/kvm/mmu/spte.c
View File

@ -22,6 +22,7 @@
bool __read_mostly enable_mmio_caching = true;
static bool __ro_after_init allow_mmio_caching;
module_param_named(mmio_caching, enable_mmio_caching, bool, 0444);
EXPORT_SYMBOL_GPL(enable_mmio_caching);
u64 __read_mostly shadow_host_writable_mask;
u64 __read_mostly shadow_mmu_writable_mask;

2
arch/x86/kvm/mmu/spte.h
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@ -5,8 +5,6 @@
#include "mmu_internal.h"
extern bool __read_mostly enable_mmio_caching;
/*
* A MMU present SPTE is backed by actual memory and may or may not be present
* in hardware. E.g. MMIO SPTEs are not considered present. Use bit 11, as it

10
arch/x86/kvm/svm/sev.c
View File

@ -22,6 +22,7 @@
#include <asm/trapnr.h>
#include <asm/fpu/xcr.h>
#include "mmu.h"
#include "x86.h"
#include "svm.h"
#include "svm_ops.h"
@ -2221,6 +2222,15 @@ void __init sev_hardware_setup(void)
if (!sev_es_enabled)
goto out;
/*
* SEV-ES requires MMIO caching as KVM doesn't have access to the guest
* instruction stream, i.e. can't emulate in response to a #NPF and
* instead relies on #NPF(RSVD) being reflected into the guest as #VC
* (the guest can then do a #VMGEXIT to request MMIO emulation).
*/
if (!enable_mmio_caching)
goto out;
/* Does the CPU support SEV-ES? */
if (!boot_cpu_has(X86_FEATURE_SEV_ES))
goto out;

9
arch/x86/kvm/svm/svm.c
View File

@ -5034,13 +5034,16 @@ static __init int svm_hardware_setup(void)
/* Setup shadow_me_value and shadow_me_mask */
kvm_mmu_set_me_spte_mask(sme_me_mask, sme_me_mask);
/* Note, SEV setup consumes npt_enabled. */
svm_adjust_mmio_mask();
/*
* Note, SEV setup consumes npt_enabled and enable_mmio_caching (which
* may be modified by svm_adjust_mmio_mask()).
*/
sev_hardware_setup();
svm_hv_hardware_setup();
svm_adjust_mmio_mask();
for_each_possible_cpu(cpu) {
r = svm_cpu_init(cpu);
if (r)