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Wed, 11 Nov 2026 14:37:05 -0800 (PST) DKIM-Filter: OpenDKIM Filter v2.11.0 linux.microsoft.com 53D8220B7166 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.microsoft.com; s=default; t=1794436648; bh=iJrORkTKZetlPYnGNZA/pkmKUZubavEmrWi57SbUmv4=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=dPZKH9zMDVcGATZlXDqvy/tVc2lf0uR4VyrTZtKpNH5QXkZiZQLnP/VcBimx5FE3T uImY8EV0e5m9I7fZIdCYLSIXQM4O815KVDGahs5UYll1dCfNWKY1zQIbJjL/uWjHQl mGkTB7JbsR3zeb+Wah0rI/ZBmKHIEKUd84s8Hqpg= Message-ID: <5d9dccba-61b0-4fac-8dc2-f09ce630157e@linux.microsoft.com> Date: Wed, 11 Nov 2026 14:36:57 -0800 X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v6 4/6] Drivers: hv: Mark shared memory as decrypted for CCA Realms To: Michael Kelley , "decui@microsoft.com" , "haiyangz@microsoft.com" , "wei.liu@kernel.org" , Mukesh R Cc: "arnd@arndb.de" , "catalin.marinas@arm.com" , "linux-arch@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" , "linux-hyperv@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "lpieralisi@kernel.org" , "mark.rutland@arm.com" , "sudeep.holla@kernel.org" , "thuth@redhat.com" , "will@kernel.org" References: <20261031001412.4150488-1-kameroncarr@linux.microsoft.com> <20261031001412.4150488-5-kameroncarr@linux.microsoft.com> Content-Language: en-US From: Kameron Carr In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 11/11/2026 10:01 AM, Michael Kelley wrote: > From: Kameron Carr Sent: Friday, October 30, 2026 5:14 PM >> >> In hv_common_cpu_init(), the per-CPU hypercall input/output pages need >> to be marked as decrypted (shared) for confidential VM isolation types. >> This is already done for SNP and TDX isolation; extend the same handling >> to Arm CCA Realm guests so that the host hypervisor can access the >> shared hypercall buffers. >> >> is_realm_world() is declared in include/linux/arm-rsi-cmds.h which only >> builds on arm64 (it includes ), so using it directly in >> the arch-neutral drivers/hv/hv_common.c would break the x86 build. >> Introduce a Hyper-V-specific helper following the established >> hv_isolation_type_snp() / hv_isolation_type_tdx() pattern. >> >> On architectures other than arm64 the weak default keeps the existing >> behaviour. >> >> Reviewed-by: Michael Kelley >> Signed-off-by: Kameron Carr >> --- >> arch/arm64/hyperv/mshyperv.c | 5 +++++ >> drivers/hv/hv_common.c | 17 +++++++++++++---- >> include/asm-generic/mshyperv.h | 1 + >> 3 files changed, 19 insertions(+), 4 deletions(-) >> >> diff --git a/arch/arm64/hyperv/mshyperv.c b/arch/arm64/hyperv/mshyperv.c >> index 46ab2da..da6c3aa0 100644 >> --- a/arch/arm64/hyperv/mshyperv.c >> +++ b/arch/arm64/hyperv/mshyperv.c >> @@ -182,3 +182,8 @@ bool hv_is_hyperv_initialized(void) >> return hyperv_initialized; >> } >> EXPORT_SYMBOL_GPL(hv_is_hyperv_initialized); >> + >> +bool hv_isolation_type_cca(void) >> +{ >> + return is_realm_world(); >> +} >> diff --git a/drivers/hv/hv_common.c b/drivers/hv/hv_common.c >> index 31256cb..a60c92c 100644 >> --- a/drivers/hv/hv_common.c >> +++ b/drivers/hv/hv_common.c >> @@ -476,6 +476,7 @@ int hv_common_cpu_init(unsigned int cpu) >> u64 msr_vp_index; >> gfp_t flags; >> const int pgcount = hv_output_page_exists() ? 2 : 1; >> + const size_t alloc_size = ALIGN((size_t)pgcount * HV_HYP_PAGE_SIZE, PAGE_SIZE); >> void *mem; >> int ret = 0; >> >> @@ -489,7 +490,7 @@ int hv_common_cpu_init(unsigned int cpu) >> * online and then taken offline >> */ >> if (!*inputarg) { >> - mem = kmalloc_array(pgcount, HV_HYP_PAGE_SIZE, flags); >> + mem = kmalloc(alloc_size, flags); >> if (!mem) >> return -ENOMEM; >> >> @@ -499,14 +500,16 @@ int hv_common_cpu_init(unsigned int cpu) >> } >> >> if (!ms_hyperv.paravisor_present && >> - (hv_isolation_type_snp() || hv_isolation_type_tdx())) { >> - ret = set_memory_decrypted((unsigned long)mem, pgcount); >> + (hv_isolation_type_snp() || hv_isolation_type_tdx() || >> + hv_isolation_type_cca())) { > > Could this big "if" statement use "hv_is_isolation_supported()" instead > of explicitly testing for each CoCo VM type? I ask partly because > Mukesh Rathor has just submitted a patch [1] that introduces a new > function that does something almost exactly the same as > hv_is_isolation_supported() and uses it here. > > You don't provide the non-stub hv_is_isolation_supported() until > Patch 6 of this series, but the weak stub should allow everything to > build if a bisection splits this patch series. Including your response to Mukesh for context: > Any reason not to use hv_is_isolation_supported()? Your > new function seems conceptually equivalent, though at a > detailed level it handles VBS isolation differently from > hv_is_isolation_supported(). But I don't think including > VBS isolation here is a problem since set_memory_decrypted() > is a no-op with VBS isolation. I'm not fully convinced that calling set_memory_decrypted() is always a no-op for VBS. I see that on VBS VMs, ms_hyperv_init_platform() calls hv_vtom_init(). If set_memory_decrypted() calls hv_mark_gpa_visibility(), you will try to use the inputarg before it has been initialized. Please let me know if my understanding is incorrect. -- Regards, Kameron > Michael > > [1] https://lore.kernel.org/linux-hyperv/20261111022036.351231-2-mrathor@linux.microsoft.com/ > >> + ret = set_memory_decrypted((unsigned long)mem, >> + alloc_size >> PAGE_SHIFT); >> if (ret) { >> /* It may be unsafe to free 'mem' */ >> return ret; >> } >> >> - memset(mem, 0x00, pgcount * HV_HYP_PAGE_SIZE); >> + memset(mem, 0x00, alloc_size); >> } >> >> /* >> @@ -666,6 +669,12 @@ bool __weak hv_isolation_type_tdx(void) >> } >> EXPORT_SYMBOL_GPL(hv_isolation_type_tdx); >> >> +bool __weak hv_isolation_type_cca(void) >> +{ >> + return false; >> +} >> +EXPORT_SYMBOL_GPL(hv_isolation_type_cca); >> + >> void __weak hv_setup_vmbus_handler(void (*handler)(void)) >> { >> } >> diff --git a/include/asm-generic/mshyperv.h b/include/asm-generic/mshyperv.h >> index bf601d6..1fa79ab 100644 >> --- a/include/asm-generic/mshyperv.h >> +++ b/include/asm-generic/mshyperv.h >> @@ -79,6 +79,7 @@ u64 hv_do_fast_hypercall16(u16 control, u64 input1, u64 >> input2); >> >> bool hv_isolation_type_snp(void); >> bool hv_isolation_type_tdx(void); >> +bool hv_isolation_type_cca(void); >> >> /* >> * On architectures where Hyper-V doesn't support AEOI (e.g., ARM64), >> -- >> 2.45.4 >>