[PATCH v2 03/39] xen/riscv: set the guest's XLEN explicitly in hstatus.VSXL

[Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>]

hstatus.VSXL is WARL, so its reset value is implementation-defined. Xen
supports 64-bit guests only, so program it explicitly instead of relying
on whatever the hardware happens to leave there.

This matters beyond the guest's own view of itself: decoding a trapped
instruction depends on the effective XLEN of the guest, as the encodings
which exist for XLEN=64 only must not be recognized for a 32-bit one.

Signed-off-by: Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>
---
Changes in v2:
 - new patch
---
---
 xen/arch/riscv/domain.c                     | 8 +++++++-
 xen/arch/riscv/include/asm/riscv_encoding.h | 2 ++
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/xen/arch/riscv/domain.c b/xen/arch/riscv/domain.c
index d94652809e36..57c37cb2dfc2 100644
--- a/xen/arch/riscv/domain.c
+++ b/xen/arch/riscv/domain.c
@@ -88,7 +88,13 @@ static void vcpu_csr_init(struct vcpu *v)
 {
     v->arch.hedeleg = HEDELEG_DEFAULT & csr_masks.hedeleg;
 
-    vcpu_guest_cpu_user_regs(v)->hstatus = HSTATUS_SPV | HSTATUS_SPVP;
+    /*
+     * Xen supports 64-bit guests only, so set the guest's XLEN explicitly
+     * rather than leaving it to the WARL behaviour of hstatus.VSXL, which the
+     * decoding of a trapped instruction depends on.
+     */
+    vcpu_guest_cpu_user_regs(v)->hstatus =
+        HSTATUS_SPV | HSTATUS_SPVP | MASK_INSR(HSTATUS_VSXL_64, HSTATUS_VSXL);
 
     v->arch.hideleg = HIDELEG_DEFAULT & csr_masks.hideleg;
 
diff --git a/xen/arch/riscv/include/asm/riscv_encoding.h 
b/xen/arch/riscv/include/asm/riscv_encoding.h
index 03e186bcdb8c..c63e5e304691 100644
--- a/xen/arch/riscv/include/asm/riscv_encoding.h
+++ b/xen/arch/riscv/include/asm/riscv_encoding.h
@@ -68,6 +68,8 @@
 #if __riscv_xlen == 64
 #define HSTATUS_VSXL                   _UL(0x300000000)
 #define HSTATUS_VSXL_SHIFT             32
+#define HSTATUS_VSXL_64                        _UL(2)
+#define HSTATUS_VSXL_32                        _UL(1)
 #endif
 #define HSTATUS_VTSR                   _UL(0x00400000)
 #define HSTATUS_VTW                    _UL(0x00200000)
-- 
2.55.0