From: Vladimir Murzin <vladimir.murzin@arm•com>
To: Mark Rutland <mark.rutland@arm•com>
Cc: linux-arm-kernel@lists•infradead.org, kvmarm@lists•linux.dev,
broonie@kernel•org, catalin.marinas@arm•com, james.morse@arm•com,
maz@kernel•org, oupton@kernel•org, tabba@google•com,
will@kernel•org
Subject: Re: [PATCH 04/18] KVM: arm64: pkvm: Remove struct cpu_sve_state
Date: Thu, 28 May 2026 16:12:12 +0100 [thread overview]
Message-ID: <518b2b2f-53c0-4082-b764-54c0e3bc2b92@arm.com> (raw)
In-Reply-To: <ahhapwyfE7WrBCby@J2N7QTR9R3.cambridge.arm.com>
On 5/28/26 16:09, Mark Rutland wrote:
> On Wed, May 27, 2026 at 05:11:26PM +0100, Vladimir Murzin wrote:
>> On 5/27/26 17:02, Mark Rutland wrote:
>>> On Wed, May 27, 2026 at 12:58:47PM +0100, Vladimir Murzin wrote:
>>>> On 5/21/26 14:25, Mark Rutland wrote:
>>>>> -struct cpu_sve_state {
>>>>> - __u64 zcr_el1;
>>>>> -
>>>>> - /*
>>>>> - * Ordering is important since __sve_save_state/__sve_restore_state
>>>>> - * relies on it.
>>>>> - */
>>>>> - __u32 fpsr;
>>>>> - __u32 fpcr;
>>>>> -
>>>>> - /* Must be SVE_VQ_BYTES (128 bit) aligned. */
>>>>> - __u8 sve_regs[];
>>>> It seems that the requirement (driven by SVE ldr/str) is
>>>> satisfied with the new sve_regs pointing to the start of the
>>>> page.
>>>>
>>>> I'm not sure whether we want to keep the comment (or perhaps
>>>> enforce this with explicit checks) so that future refactoring
>>>> doesn't lead to time spent debugging alignment faults...
>>> AFAICT alignment has never been functionally necessary. The LDR (vector)
>>> and STR (vector) instructions only mandate alignment when the relevant
>>> SCTLR_ELx has SCTLR_ELx.A==1. For kernel and hyp code we configure
>>> SCTLR_ELx.A==0, so there's no alignment requirement.
>>>
>>> Per ARM DDI 0487 M.b, section C8.2.437 "LDR (vector)":
>>>
>>> The load is performed as contiguous byte accesses, with no endian
>>> conversion and no guarantee of single-copy atomicity larger than a
>>> byte. However, *if alignment is checked*, then the base register must be
>>> aligned to 16 bytes.
>>>
>>> Per ARM DDI 0487 M.b, section C8.2.777 "STR (vector)":
>>>
>>> The store is performed as contiguous byte accesses, with no endian
>>> conversion and no guarantee of single-copy atomicity larger than a
>>> byte. However, *if alignment is checked*, then the base register must be
>>> aligned to 16 bytes.
>>>
>>> ... and in both cases the pseudocode shows that AlignmentEnforced()
>>> depends on the value of SCTLR_ELx.A.
>>>
>>> Given that, I don't think we need the comment.
>>>
>> Thanks for explanation! Maybe worth mentioning in commit message that it never was
>> a requirement?
> I've added the following to the commi message:
>
> I've dropped the comment regarding buffer alignment as AFAICT this was
> never necessary. The LDR/STR (vector) instructions only require this
> alignment when SCTLR_ELx.A==1, which is not the case for the kernel or
> hyp code. Nothing else depends on the alignment.
>
Brilliant!
Thanks
Vladimir
> Mark.
>
next prev parent reply other threads:[~2026-05-28 15:12 UTC|newest]
Thread overview: 78+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-05-21 13:25 [PATCH 00/18] arm64+KVM: FPSIMD/SVE/SME cleanups Mark Rutland
2026-05-21 13:25 ` [PATCH 01/18] KVM: arm64: Don't include <asm/fpsimdmacros.h> Mark Rutland
2026-05-26 14:18 ` Mark Brown
2026-05-27 10:10 ` Vladimir Murzin
2026-05-21 13:25 ` [PATCH 02/18] KVM: arm64: Don't override FFR save/restore argument Mark Rutland
2026-05-26 14:27 ` Mark Brown
2026-05-27 10:16 ` Vladimir Murzin
2026-05-21 13:25 ` [PATCH 03/18] KVM: arm64: pkvm: Save host FPMR in host cpu context Mark Rutland
2026-05-27 10:29 ` Vladimir Murzin
2026-05-21 13:25 ` [PATCH 04/18] KVM: arm64: pkvm: Remove struct cpu_sve_state Mark Rutland
2026-05-27 11:58 ` Vladimir Murzin
2026-05-27 16:02 ` Mark Rutland
2026-05-27 16:11 ` Vladimir Murzin
2026-05-28 15:09 ` Mark Rutland
2026-05-28 15:12 ` Vladimir Murzin [this message]
2026-05-21 13:25 ` [PATCH 05/18] arm64: fpsimd: Fold sve_init_regs() into do_sve_acc() Mark Rutland
2026-05-26 15:28 ` Mark Brown
2026-05-27 12:05 ` Vladimir Murzin
2026-05-21 13:25 ` [PATCH 06/18] arm64: fpsimd: Remove sve_set_vq() and sme_set_vq() Mark Rutland
2026-05-26 15:42 ` Mark Brown
2026-05-27 12:50 ` Vladimir Murzin
2026-05-21 13:25 ` [PATCH 07/18] arm64: fpsimd: Use assembler for SVE instructions Mark Rutland
2026-05-26 15:43 ` Mark Brown
2026-05-27 12:58 ` Vladimir Murzin
2026-05-27 16:10 ` Mark Rutland
2026-05-21 13:25 ` [PATCH 08/18] arm64: fpsimd: Use assembler for baseline SME instructions Mark Rutland
2026-05-26 15:45 ` Mark Brown
2026-05-27 13:06 ` Vladimir Murzin
2026-05-21 13:25 ` [PATCH 09/18] arm64: fpsimd: Move sve_get_vl() and sme_get_vl() inline Mark Rutland
2026-05-26 15:47 ` Mark Brown
2026-05-27 13:18 ` Vladimir Murzin
2026-05-21 13:25 ` [PATCH 10/18] arm64: sysreg: Add FPCR and FPSR Mark Rutland
2026-05-26 15:55 ` Mark Brown
2026-05-26 16:51 ` Mark Rutland
2026-05-26 16:54 ` Mark Brown
2026-05-21 13:25 ` [PATCH 11/18] arm64: fpsimd: Split FPSR/FPCR from SVE save/restore Mark Rutland
2026-05-26 16:28 ` Mark Brown
2026-05-27 13:51 ` Mark Rutland
2026-05-27 14:13 ` Mark Brown
2026-05-27 16:13 ` Mark Rutland
2026-05-27 13:44 ` Vladimir Murzin
2026-05-21 13:25 ` [PATCH 12/18] arm64: fpsimd: Move fpsimd save/restore inline Mark Rutland
2026-05-26 16:44 ` Mark Brown
2026-05-28 16:15 ` Mark Rutland
2026-05-28 16:39 ` Mark Brown
2026-05-27 14:49 ` Vladimir Murzin
2026-05-27 15:34 ` Mark Rutland
2026-05-27 16:13 ` Vladimir Murzin
2026-05-21 13:25 ` [PATCH 13/18] arm64: fpsimd: Use opaque type for SVE state Mark Rutland
2026-05-26 16:53 ` Mark Brown
2026-05-28 9:45 ` Vladimir Murzin
2026-05-28 16:25 ` Mark Rutland
2026-05-21 13:25 ` [PATCH 14/18] arm64: fpsimd: Use opaque type for SME state Mark Rutland
2026-05-26 16:56 ` Mark Brown
2026-05-28 9:51 ` Vladimir Murzin
2026-05-21 13:25 ` [PATCH 15/18] arm64: fpsimd: Move SVE save/restore inline Mark Rutland
2026-05-27 12:29 ` Mark Brown
2026-05-28 10:39 ` Vladimir Murzin
2026-05-21 13:25 ` [PATCH 16/18] arm64: fpsimd: Move sve_flush_live() inline Mark Rutland
2026-05-27 12:54 ` Mark Brown
2026-05-27 16:23 ` Mark Rutland
2026-05-28 10:49 ` Vladimir Murzin
2026-05-21 13:25 ` [PATCH 17/18] arm64: fpsimd: Move SME save/restore inline Mark Rutland
2026-05-26 14:08 ` Mark Rutland
2026-05-26 14:39 ` Vladimir Murzin
2026-05-26 15:28 ` Mark Rutland
2026-05-26 16:38 ` Mark Rutland
2026-05-27 9:00 ` Vladimir Murzin
2026-05-29 9:10 ` Mark Rutland
2026-05-28 12:30 ` Vladimir Murzin
2026-05-28 14:39 ` Mark Rutland
2026-05-21 13:25 ` [PATCH 18/18] arm64: fpsimd: Remove <asm/fpsimdmacros.h> Mark Rutland
2026-05-28 13:10 ` Vladimir Murzin
2026-05-27 8:07 ` [PATCH 00/18] arm64+KVM: FPSIMD/SVE/SME cleanups Marc Zyngier
2026-05-27 10:32 ` Mark Rutland
2026-05-27 14:36 ` Will Deacon
2026-05-28 13:21 ` Vladimir Murzin
2026-05-28 16:28 ` Mark Rutland
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