Commit c3e0c8c2 authored by Sean Christopherson's avatar Sean Christopherson Committed by Paolo Bonzini
Browse files

KVM: x86/mmu: Fully re-evaluate MMIO caching when SPTE masks change 



Fully re-evaluate whether or not MMIO caching can be enabled when SPTE
masks change; simply clearing enable_mmio_caching when a configuration
isn't compatible with caching fails to handle the scenario where the
masks are updated, e.g. by VMX for EPT or by SVM to account for the C-bit
location, and toggle compatibility from false=>true.

Snapshot the original module param so that re-evaluating MMIO caching
preserves userspace's desire to allow caching.  Use a snapshot approach
so that enable_mmio_caching still reflects KVM's actual behavior.

Fixes: 8b9e74bf ("KVM: x86/mmu: Use enable_mmio_caching to track if MMIO caching is enabled")
Reported-by: default avatarMichael Roth <michael.roth@amd.com>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Cc: stable@vger.kernel.org
Tested-by: default avatarMichael Roth <michael.roth@amd.com>
Signed-off-by: default avatarSean Christopherson <seanjc@google.com>
Reviewed-by: default avatarKai Huang <kai.huang@intel.com>
Message-Id: <20220803224957.1285926-3-seanjc@google.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent 982bae43

arch/x86/kvm/mmu/mmu.c

+4 −0
Original line number Diff line number Diff line
@@ -6697,11 +6697,15 @@ static int set_nx_huge_pages(const char *val, const struct kernel_param *kp) 
/*

 * nx_huge_pages needs to be resolved to true/false when kvm.ko is loaded, as

 * its default value of -1 is technically undefined behavior for a boolean.

 * Forward the module init call to SPTE code so that it too can handle module

 * params that need to be resolved/snapshot.

 */

void __init kvm_mmu_x86_module_init(void)

{

	if (nx_huge_pages == -1)

		__set_nx_huge_pages(get_nx_auto_mode());



	kvm_mmu_spte_module_init();

}



/*

arch/x86/kvm/mmu/spte.c

+19 −0
Original line number Diff line number Diff line
@@ -20,6 +20,7 @@ 
#include <asm/vmx.h>



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);



u64 __read_mostly shadow_host_writable_mask;
@@ -43,6 +44,18 @@ u64 __read_mostly shadow_nonpresent_or_rsvd_lower_gfn_mask; 


u8 __read_mostly shadow_phys_bits;



void __init kvm_mmu_spte_module_init(void)

{

	/*

	 * Snapshot userspace's desire to allow MMIO caching.  Whether or not

	 * KVM can actually enable MMIO caching depends on vendor-specific

	 * hardware capabilities and other module params that can't be resolved

	 * until the vendor module is loaded, i.e. enable_mmio_caching can and

	 * will change when the vendor module is (re)loaded.

	 */

	allow_mmio_caching = enable_mmio_caching;

}



static u64 generation_mmio_spte_mask(u64 gen)

{

	u64 mask;
@@ -340,6 +353,12 @@ void kvm_mmu_set_mmio_spte_mask(u64 mmio_value, u64 mmio_mask, u64 access_mask) 
	BUG_ON((u64)(unsigned)access_mask != access_mask);

	WARN_ON(mmio_value & shadow_nonpresent_or_rsvd_lower_gfn_mask);



	/*

	 * Reset to the original module param value to honor userspace's desire

	 * to (dis)allow MMIO caching.  Update the param itself so that

	 * userspace can see whether or not KVM is actually using MMIO caching.

	 */

	enable_mmio_caching = allow_mmio_caching;

	if (!enable_mmio_caching)

		mmio_value = 0;

arch/x86/kvm/mmu/spte.h

+1 −0
Original line number Diff line number Diff line
@@ -450,6 +450,7 @@ static inline u64 restore_acc_track_spte(u64 spte) 


u64 kvm_mmu_changed_pte_notifier_make_spte(u64 old_spte, kvm_pfn_t new_pfn);



void __init kvm_mmu_spte_module_init(void);

void kvm_mmu_reset_all_pte_masks(void);



#endif