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KVM: arm64: Make the exposed feature bits in AA64DFR0_EL1 writable from userspace

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KVM exposes the OS double lock feature bit to Guests but returns
RAZ/WI on Guest OSDLR_EL1 access. This breaks Guest migration between
systems where this feature differ. Add support to make this feature
writable from userspace by setting the mask bit. While at it, set the
mask bits for the exposed WRPs(Number of Watchpoints) as well.
Also update the selftest to cover these fields.

However we still can't make BRPs and CTX_CMPs fields writable, because
as per ARM ARM DDI 0487K.a, section D2.8.3 Breakpoint types and
linking of breakpoints, highest numbered breakpoints(BRPs) must be
context aware breakpoints(CTX_CMPs). KVM does not trap + emulate the
breakpoint registers, and as such cannot support a layout that misaligns
with the underlying hardware.

Reviewed-by: Oliver Upton <oliver.upton@linux.dev>
Signed-off-by: Shameer Kolothum <shameerali.kolothum.thodi@huawei.com>
Link: https://lore.kernel.org/r/20240816132819.34316-1-shameerali.kolothum.thodi@huawei.com
Signed-off-by: Marc Zyngier <maz@kernel.org>
This commit is contained in:
Shameer Kolothum
2024-08-16 14:28:19 +01:00
committed by Marc Zyngier
parent 7c626ce4ba
commit 980c41f554
2 changed files with 17 additions and 1 deletions
Download Patch File Download Diff File Expand all files Collapse all files
arch/arm64/kvm/sys_regs.c
+15 -1
View File
@@ -2376,7 +2376,21 @@ static const struct sys_reg_desc sys_reg_descs[] = {
.get_user = get_id_reg,
.set_user = set_id_aa64dfr0_el1,
.reset = read_sanitised_id_aa64dfr0_el1,
.val = ID_AA64DFR0_EL1_PMUVer_MASK |
/*
* Prior to FEAT_Debugv8.9, the architecture defines context-aware
* breakpoints (CTX_CMPs) as the highest numbered breakpoints (BRPs).
* KVM does not trap + emulate the breakpoint registers, and as such
* cannot support a layout that misaligns with the underlying hardware.
* While it may be possible to describe a subset that aligns with
* hardware, just prevent changes to BRPs and CTX_CMPs altogether for
* simplicity.
*
* See DDI0487K.a, section D2.8.3 Breakpoint types and linking
* of breakpoints for more details.
*/
.val = ID_AA64DFR0_EL1_DoubleLock_MASK |
ID_AA64DFR0_EL1_WRPs_MASK |
ID_AA64DFR0_EL1_PMUVer_MASK |
ID_AA64DFR0_EL1_DebugVer_MASK, },
ID_SANITISED(ID_AA64DFR1_EL1),
ID_UNALLOCATED(5,2),
tools/testing/selftests/kvm/aarch64/set_id_regs.c
+2
View File
@@ -68,6 +68,8 @@ struct test_feature_reg {
}
static const struct reg_ftr_bits ftr_id_aa64dfr0_el1[] = {
S_REG_FTR_BITS(FTR_LOWER_SAFE, ID_AA64DFR0_EL1, DoubleLock, 0),
REG_FTR_BITS(FTR_LOWER_SAFE, ID_AA64DFR0_EL1, WRPs, 0),
S_REG_FTR_BITS(FTR_LOWER_SAFE, ID_AA64DFR0_EL1, PMUVer, 0),
REG_FTR_BITS(FTR_LOWER_SAFE, ID_AA64DFR0_EL1, DebugVer, ID_AA64DFR0_EL1_DebugVer_IMP),
REG_FTR_END,