Re: [PATCH] KVM: x86/xen: Use hva_t for holding hypercall page address

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On 08/02/21 21:15, Sean Christopherson wrote:
Use hva_t, a.k.a. unsigned long, for the local variable that holds the
hypercall page address.  On 32-bit KVM, gcc complains about using a u64
due to the implicit cast from a 64-bit value to a 32-bit pointer.

   arch/x86/kvm/xen.c: In function ‘kvm_xen_write_hypercall_page’:
   arch/x86/kvm/xen.c:300:22: error: cast to pointer from integer of
                              different size [-Werror=int-to-pointer-cast]
   300 |   page = memdup_user((u8 __user *)blob_addr, PAGE_SIZE);

Cc: Joao Martins <joao.m.martins@xxxxxxxxxx>
Cc: David Woodhouse <dwmw@xxxxxxxxxxxx>
Fixes: 23200b7a30de ("KVM: x86/xen: intercept xen hypercalls if enabled")
Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
---
  arch/x86/kvm/xen.c | 8 ++++++--
  1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/xen.c b/arch/x86/kvm/xen.c
index 2cee0376455c..deda1ba8c18a 100644
--- a/arch/x86/kvm/xen.c
+++ b/arch/x86/kvm/xen.c
@@ -286,8 +286,12 @@ int kvm_xen_write_hypercall_page(struct kvm_vcpu *vcpu, u64 data)
  				return 1;
  		}
  	} else {
-		u64 blob_addr = lm ? kvm->arch.xen_hvm_config.blob_addr_64
-				   : kvm->arch.xen_hvm_config.blob_addr_32;
+		/*
+		 * Note, truncation is a non-issue as 'lm' is guaranteed to be
+		 * false for a 32-bit kernel, i.e. when hva_t is only 4 bytes.
+		 */
+		hva_t blob_addr = lm ? kvm->arch.xen_hvm_config.blob_addr_64
+				     : kvm->arch.xen_hvm_config.blob_addr_32;
  		u8 blob_size = lm ? kvm->arch.xen_hvm_config.blob_size_64
  				  : kvm->arch.xen_hvm_config.blob_size_32;
  		u8 *page;


Queued, thanks.

Paolo




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