linux-kernel - [PATCH v11 05/16] KVM: x86/mmu: Drop non-PA bits when getting GFN for guest's PGD

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Message-Id: <20230913124227.12574-6-binbin.wu@linux.intel.com>
Date:   Wed, 13 Sep 2023 20:42:16 +0800
From:   Binbin Wu <binbin.wu@...ux.intel.com>
To:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     seanjc@...gle.com, pbonzini@...hat.com, chao.gao@...el.com,
        kai.huang@...el.com, David.Laight@...LAB.COM,
        robert.hu@...ux.intel.com, guang.zeng@...el.com,
        binbin.wu@...ux.intel.com
Subject: [PATCH v11 05/16] KVM: x86/mmu: Drop non-PA bits when getting GFN for guest's PGD

Drop non-PA bits when getting GFN for guest's PGD with the maximum theoretical
mask for guest MAXPHYADDR.

Do it unconditionally because it's harmless for 32-bit guests, querying 64-bit
mode would be more expensive, and for EPT the mask isn't tied to guest mode.
Using PT_BASE_ADDR_MASK would be technically wrong (PAE paging has 64-bit
elements _excpet_ for CR3, which has only 32 valid bits), it wouldn't matter
in practice though.

Opportunistically use GENMASK_ULL() to define __PT_BASE_ADDR_MASK.

Signed-off-by: Binbin Wu <binbin.wu@...ux.intel.com>
Tested-by: Xuelian Guo <xuelian.guo@...el.com>
---
 arch/x86/kvm/mmu/mmu.c          | 2 +-
 arch/x86/kvm/mmu/mmu_internal.h | 1 +
 arch/x86/kvm/mmu/paging_tmpl.h  | 2 +-
 3 files changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index e1d011c67cc6..f316df038e61 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -3774,7 +3774,7 @@ static int mmu_alloc_shadow_roots(struct kvm_vcpu *vcpu)
 	hpa_t root;
 
 	root_pgd = kvm_mmu_get_guest_pgd(vcpu, mmu);
-	root_gfn = root_pgd >> PAGE_SHIFT;
+	root_gfn = (root_pgd & __PT_BASE_ADDR_MASK) >> PAGE_SHIFT;
 
 	if (!kvm_vcpu_is_visible_gfn(vcpu, root_gfn)) {
 		mmu->root.hpa = kvm_mmu_get_dummy_root();
diff --git a/arch/x86/kvm/mmu/mmu_internal.h b/arch/x86/kvm/mmu/mmu_internal.h
index b102014e2c60..b5aca7560fd0 100644
--- a/arch/x86/kvm/mmu/mmu_internal.h
+++ b/arch/x86/kvm/mmu/mmu_internal.h
@@ -13,6 +13,7 @@
 #endif
 
 /* Page table builder macros common to shadow (host) PTEs and guest PTEs. */
+#define __PT_BASE_ADDR_MASK GENMASK_ULL(51, 12)
 #define __PT_LEVEL_SHIFT(level, bits_per_level)	\
 	(PAGE_SHIFT + ((level) - 1) * (bits_per_level))
 #define __PT_INDEX(address, level, bits_per_level) \
diff --git a/arch/x86/kvm/mmu/paging_tmpl.h b/arch/x86/kvm/mmu/paging_tmpl.h
index c85255073f67..4d4e98fe4f35 100644
--- a/arch/x86/kvm/mmu/paging_tmpl.h
+++ b/arch/x86/kvm/mmu/paging_tmpl.h
@@ -62,7 +62,7 @@
 #endif
 
 /* Common logic, but per-type values.  These also need to be undefined. */
-#define PT_BASE_ADDR_MASK	((pt_element_t)(((1ULL << 52) - 1) & ~(u64)(PAGE_SIZE-1)))
+#define PT_BASE_ADDR_MASK	((pt_element_t)__PT_BASE_ADDR_MASK)
 #define PT_LVL_ADDR_MASK(lvl)	__PT_LVL_ADDR_MASK(PT_BASE_ADDR_MASK, lvl, PT_LEVEL_BITS)
 #define PT_LVL_OFFSET_MASK(lvl)	__PT_LVL_OFFSET_MASK(PT_BASE_ADDR_MASK, lvl, PT_LEVEL_BITS)
 #define PT_INDEX(addr, lvl)	__PT_INDEX(addr, lvl, PT_LEVEL_BITS)
-- 
2.25.1